Back when I was writing and producing Dharma and Greg, the only way to read my cards was to record each episode on a VCR and hit the "pause" button. This was not an easy task. The image wobbled like crazy making the tiny words of my weekly tomes very hard to see.
In video, sometimes the screen will show something briefly that you cannot tell what it is unless you play the video in slow motion or pause it. Often it turns out to be a joke or a Shout-Out.
Unreadably Fast Text is a subtrope of this.
Also called a "Blink And You'll Miss It" moment.
(It's often good to link to pictures or actually describe what's seen when giving examples of this trope.)
Compare Easter Egg, Blipvert, and (when it happens in-story) Subliminal Seduction.
30 Seconds to Mars' Attack video, by way of superimposed writing and scribblings. Probably the only one in recorded history to use this to give a Shout-Out to their fanbase and equate the lead singer to Satan within the same timespan.
Specifically invoked in the Matthew Good video for Weapon. Initially upset with what the video's director had done with it, Good took control of the project and inserted every-other-frame videos, very quick flashes of words, and actually lengthy diatribes that you have to pause to be able to read. The video won a Juno (the Canadian Grammy), but because Good boycotts the Junos, the original director accepted the award...despite not really making it in the first place.
The All-American Rejects' "Dirty Little Secret" video features people who's faces are hidden by little cards that admit their dirty little secret, such as suspecting that their fiancee isn't the One or exactly what happened at church camp...
Kennedy's "Mama Made Me a Pimp" features a split-second flash of a skull in the mirror, foreshadowing the protagonist getting killed in a knife fight by a rival pimp.
Shooting Disaster Drop in White Water plays an animation showing water rushing towards the viewer; for one frame, a cow appears in the lower-left corner.
Safe Cracker: When you get into the vault through the cellar, the animation that plays has Brian Morrison's initials pop up very briefly on the far right side.
In the scene in Metal Gear Awesome where the player skips the long cutscene, slowing it down reveals some very strange drawings, and a screen with the handwritten text 'I wish people could see these drawings, I think they're pretty funny'.
Every so often in Happy Tree Friends episodes from 2012 onwards you will see a quick cameo from a rejected character Truffles the pig, sometimes he can be seen among the dead, in a pile of junk or debris, and on one occasion when Flaky exploded he can briefly be seem flying out of her.
Sometimes in Space Tree, a long shot of a character talking will have a different image show for a frame. Random bits of text are also often displayed, though longer and more subtly than the usual freeze frame bonus.
"Really? You went to read this knowing it would lead you straight to hell? What the Ass-Puke is wrong with you? It's friggin' Hell! Fire, pain, the Devil, it's worth that to see what this said? That Guy With The Glasses was just kidding when he said you were going to Hell, but now that you've actually come back to pause it, we have no choice. You're going to Lem. It's a place like Hell but ten times worse. It's not written about in the Bible because every time some one tried writing about it, they'd cut their own head off. It's THAT bad. So I hope it was worth it, I hope it was worth pausing this video for that. See ya in Lem ya miserable piece of donkey rectum. En- friggin- joy!"
In the "Top 11 Avatars" episode, the first page of the "Cab Bitches" book has two entire paragraphs, including these lines:
Do you really think anyone's going to be attracted to you when you say "Oh yeah, I pause online videos to see if they put in secret jokes?" God, I'm surprised several women haven't just stripped naked shouting "Take me!" from reading that line. Jesus Christ! We'll spare you from pausing the video to look up any any other secrets, because there aren't any.
In Dead Fantasy Part V, the flickering in Tifa's flashback conceals text. Also, pausing at the moment right after Hayate knocks Tifa out will show a very, very brief image of a white materia in the middle of her back.
Also, all of Hayate's attacks and movements are animated - they just move so fast that they look like he's teleporting. You have to actually go through the video frame-by-frame to see what he's doing.
A fan ending to Botchamania episode 166 (which uses voice clips from NFL Blitz 2001) has a bunch of these. Interspersed with images of random wrestlers and WrestleCrap moments, there are a few jokes written about them that can only be seen on the screen for a fraction of a second (example: the announcer calls out "Fat" while showing an image of Samoa Joe, and the caption above Joe's head reads "Damn you, Scott Steiner promos! And your unintentional hilarity!" note a reference to an interview from 2009 where Steiner calls Joe a "fat slob")
Pinisu-chan's essay in the first episode of Large Bagel begins with her trying to find out where she came from and if there are other Large Bagel's, only to change in the second paragraph to a Prince Of Bel Air parody.
In Paranoia Drift, an AMV that retells The Girl Who Leapt Through Time as delusions from Makoto's mind, there are a few frames at the beginning which read "This time while watching this video please remove all your emotional and logical effliction to this anime".
5 Second Films does a lot of "Blink and Your Miss It" jokes. For example in "Meanwhile, in Kansas", the headline of the newspaper at the end reads, "Don't Enter Politics. It Can Turn Your Daughter Gay!"
Used as foreshadowing in To Boldly Flee. When The Nostalgia Critic finds out the dialog he just spoke was written for him, we see the flash of script and realize that he didn't follow it to the letter. This sets up the gist of the next few scenes; that he's evolved and has taken control of his own character.
Community Channel has been doing this in her videos recently, because people kept pausing to read the fake webpages. Now they usually start with text that's relevant to the subject, cut off mid-sentence by "why do you guys pause the videos to read these" or something similar.
This is a running gag with every Solar Flare producing a different flash. Other instances include Dodria's head on a large woman showering; Lanipator in drag; and two insects mating.
Mr. Mendo'sreview of a horrible porn flick culminates in a jumbled sequence (from the original film) covered with various censorship signs and captions. Towards the end, for a split-second, there's a caption that reads: "I'm willing to worship whatever deity makes this Slipknot editing go the fuck away!"
When Chaotrix is hacking the Student Database in Super Academy, we get some glimpses of everyone's class lists. Without exception, every single student is registered for the class "Reading and Writing 1".
In Matthew Santoro's video about the group Anonymous, you can see that Matt is wearing the Guy Fawkes mask worn by the members of Anonymous at various points in the video.
In Rainbow Dashs Precious Book, there's a scene in Part 5 where the human character books a flight to escape from Rainbow Dash. While the plane takes off from its runway, a filly speculated to be either Scootaloo (who appeared earlier in the episode) or Babs Seed can be briefly spotted on the runway.