Animal Stereotypes: The farm animals have about human-level intelligence, but the sheep are dim and easily led, Bitzer regards his master with appropriately doglike devotion, the pigs are greedy and superior, the cat is evil, etc.
Anthropomorphic Shift: Shaun and most of the other sheep in "A Close Shave" were portrayed as more brainless, realistic acting animals with more subtle human-like traits. In the series, Shaun (and to an extent the other sheep) are almost on par with Gromit in terms of anthro traits, often walking on two legs, using their front feet as hands or making similar human-like facial expressions. The degree of shift differs between the "farm animals" and the likes of Bitzer and Pidsley. The farm animals are essentially anthro except when the farmer is looking, while both Bitzer and Pidsley have realistic behavioral weaknesses in the form of Bitzer's unavoidable reversion to doglike behavior (including the disappearance of his wristwatch) whenever a stick is thrown, and Pidsley's involuntary reaction to being presented with a ball of yarn. These flaws are mercilessly exploited by the sheep and numerous other characters.
Art Shift: Some of the new character models, particularly that of Bitzer the sheepdog in the most recent series are quite noticeably different. The replacements were made because of a combination of wear on the old ones and technical improvements, for the record.
Although it's also clear that the main characters were given easily swappable mouths to speed up production.
The updated models were primarily due to the switch to HD video, which made fingerprints in materials previously used too obvious. The new materials appear to hold detail better, hence the addition of details like Bitzer's "fur"
Dropped Abridge On Him: When shown on the Disney channel in the US, most episodes were heavily edited and ended up being of very variable length. Most of the edits concerned the realistically dropping-strewn field that the sheep inhabit as well as instances of Toilet Humour. Some, such as the scene in "We Wish Ewe A Merry Xmas" where the farmer straightens the head on the snowman, which promptly falls off appear to be instances of Think Of The Children. Other, more inexplicable edits were made to fit the show to its allotted slot. In some episodes, the edits were so extensive as to completely break the plot, or reduce the length of the episode to a point where other measures were taken to lengthen the episode, for example by running the opening titles at a reduced speed. This was not a format conversion artifact, since it was present on some episodes but not others.
Hammer Space: Bitzer can pull a walkie-talkie out from behind his back, and pull out his thermos no matter where he is.
Shirley's wool holds just about everything.
Hero Antagonist: Bitzer during some of the flock's mischevious moments. He just wants to keep things in order for the farmer, and is usually rather friendly to Shaun and the others when they aren't causing trouble for him. Since he usually the Butt Monkey under these moments it tends to double as Sympathetic Inspector Antagonist.
Hidden Depths: While Shirley is generally considered to be a Living Doorstop or Big Eater, she switches role to The Big Guy in "Lock Out", nailing Pidsley to the wall with a twirl of a hammer, and to Secretly Wealthy in "In The Doghouse" where she contributes several large wads of cash to pay for Bitzer's new deluxe kennel, while all of the other sheep, having no idea of even the concept of money, have contributed buttons, etc.
Idiot Houdini: No matter what the flock does, Shaun and Bitzer always save them in the end, and generally end up inconveniencing the farmer as well.
Intellectual Animal: Practically everyone on the farm. Curiously, they all fake being dumb animals while in front of the Farmer, except for Bitzer, who doesn't hide using a clipboard to track the sheep or taking his lunch with a thermos of coffee.
Fridge Brilliance: But consider this is a world where Gromit can be arrested for sheep murder (as opposed to being put down) and publishers print Electronics For Dogs handyman books. Dogs are expected to act more like humans. Besides, if the farmer knew the sheep were (on the whole) just as intelligent as Bitzer but much less loyal, he'd probably put a stop to their adventures.
Jerk Ass: The Naughty Pigs, their sty is often considered out of bounds for the flock.
Shirley, due to her knack for standing still and eating while oblivious to the world around her.
Timmy, who over the course of the two seasons has been used as a paintbrush, chalkboard eraser, table, plug for a ship's horn, pillow, curling stone, and handkerchief.
Loveable Rogue: Shaun. His schemes often involve screwing the Farmer or Bitzer in some way, but he has no harmful intent and occasionally tries to do nice things for them to compensate. Usually the rest of the flock get in on this too.
Masquerade: The sheep conceal their intelligence from the humans.
Negative Continuity: No matter what happens throughout an entire episode, everything goes back to normal in the next. Self-subverts this to an extent in that certain items (most notably hats) that are "acquired" in one episode will reappear in later episodes. Examples of this are the primary plot device of "Bitzer's New Hat", which has migrated to the sheep by "An Ill Wind", and the Russian army ushanka from "Sheepwalking", which also reappears in "An Ill Wind".
No OSHA Compliance: directly averted. Shaun always wears a mask while welding, and any animals shown using dangerous tools such as chainsaws or jackhammers are always shown wearing hardhats, safety goggles and yellow safety vests.
The primary "accented" voice in the show is that of the farmer, who is voiced by John Sparkes, who specializes in Welsh characters. The farmer's accent is clearly Welsh in the first season, but has definitely moved to Northern England by the end of the second season.
Running Gag: The farmer's blue underpants make numerous appearance, although never on the farmer. Frequently they end up on the heads of characters (usually Pidsley, although they first appear on Shirley), at which point they appear to spontaneously develop eyeholes, except when the plot requires that they don't. They also grow in size in "Lock Out" - Shirley makes use of them as a handy "cat-holder" when she nails Pidsley to the wall.
Very detailed King Kong sequence in "Supersized Timmy", with giant Timmy on the house roof holding an unconscious Bitzer while swiping at a duck that is circling his head.
Numerous montage sequences, including a faithful-to-Rockytraining montage in "Shape Up With Shaun", a similar one in "Bitzer's Basic Training", and numerous equipment assembly montages (examples in "Pig Swill Fly" and "The Magpie"), all with appropriate accompanying musical accompaniment.
A sheep stands at the front of the boat with their arms spread out, re-enacting the most famous scene of Titanic... Until another sheep knocks them off the boat with the sails.
The episode "The Big Chase" is to a large extent a homage to the final chase scene in first "The Pink Panther" movie.
"Pig Trouble" makes use of the main musical motif from "Babe".
Bitzer's musical accompaniment to the farmer's dinner date in "Frantic Romantic" is pure Liberace. The wink to the camera is also a rare instance of the series Breaking the Fourth Wall.
Astute viewers will note that Shaun's guitar amp goes up to eleven.
In "Off the Baa", the tune of Nessun dorma from Turandot can be heard playing in the background as the cabbage-football goes flying through the air, just like in Bend It Like Beckham. However, this in turn is a reference to the BBC's use of this music as the theme for their 1990 FIFA World Cup coverage.
The sequence in "Stick With Me" where Bitzer is running from a large ball of glued-together sheep references Raiders of the Lost Ark.
"Little Sheep Of Horrors" contains many suspense/horror tropes, the clearest of which is the shower scene in "Psycho".
"Alien": Averted, possibly retroactively, in "Take Away", where there's a discontinuity between the stacked sheep trying to read the map and the bystander running off in horror. The editing is very suggestive of this originally having been an "alien chest burster" parody that was either cut or written out before filming.
"Saturday Night Shaun" can be considered to contain either a reference to "Saturday Night Fever" or a reference to "Airplane!"'s reference to the same scene.
"Fawlty Towers" in "The Visitor", where the alien begins hitting his spaceship with a branch.
"Futurama", also in "The Visitor", whose spaceship ends up running on sheep droppings (which are small, round black lumps).
"Mission: Impossible": The show frequently uses a pastiche of the "Mission Impossible" theme during some of Shaun's more complex plans. Perhaps the canonical example of this occurs in "Bathtime".
"A Grand Day Out" - Aardman get self-referential in "Troublesome Tractor", in which Timmy has exactly the same problem with a power drill as Gromit did in "A Grand Day Out".
During the second season, a pastiche of "Yakety Sax", as used in every The Benny Hill Show chase scene ever, is played over some chase scenes. Notable examples in "Bitzer From The Black Lagoon" and "Cock-a-Doodle Shaun".
The first scene of "Cat Got Your Brain", showing the silent shadow of the alien saucer moving over the farm, accompanied by a low rumble, is clearly ""Independence Day"-inspired, although it's technically a little more realistic since British farms do not suffer from Space Is Noisy.
Although not part of the series proper, the music video that accompanied the release of an extended version of the opening theme tune ("Life's A Treat" by Vic Reeves) contains many clear references to the music videos of Madness such as their trademark "nutty dance", fezzes and a flying saxophonist suspending from a wire.
The Speechless: Everybody. The animals bleat, grunt and bark respectively, and even the humans speak an unintelligble Simlish. This slips slightly in the later episodes from the second season - the farmer's accent shift coincides with his becoming borderline intelligible (albeit for only a word or two) and Shaun's own voice changes slightly from "always a sheep" to sounding human in when it comes to screams, cheers, etc. Even Talking With Signs is avoided and printed material shown in the show is either solely pictorial or conveys no information through the text (which is often nonsense words, with letters sometimes mirrored or inverted).
Toon Physics: Many standard examples, such as characters being briefly suspended in air before falling, and various items being launched into the air to implausibly high altitudes, or staying up for an improbably long time.
Torches and Pitchforks: In the episode "Supersized Timmy" although the trope is subverted somewhat by one of the "villagers" turning up with a lamp rather than a torch.