Cast the Expert: The doctors are real doctors. The commentary mentions that this was because actors wouldn't quite speak as if they had been using the proper terms for years because, well, they hadn't been.
Cross-Dressing Voices: Played straight with E.T. in the original version and in the Japanese dub, but averted in the Mexican Spanish dub.
Deleted Scene: Harrison Ford filmed a scene as the principal of Elliot's school, set after he frees the frogs, which Spielberg cut because he felt Ford's presence was too distracting.
Two deleted scenes were reinstated for the 20th Anniversary Elliot shows E.T. the bathroom and gets a call from his mother. E.T. plays around in the bathtub, which Elliot thinks he's drowning. Turns out he was having fun. The other one shows Mary finding Mike and Gertie during trick or treating, Gertie spills the beans on where Elliot is, and she tells them to get in the car.
There was a subplot cut where E.T. was in love with Elliot's mom. He goes into her room and leaves a Reese's Pieces on her pillow.
There's a scene of when E.T.'s getting Elliot drunk. Elliot gets sent to the nurse's office and writes the plans for the communicator on the wall.
There was originally an alternate ending showing the boys playingDungeons & Dragons with Elliot as the dungeon master. The camera pans up to the roof, where the communicator is calling out to E.T.
Enforced Method Acting: When Gertie bursts in on Elliot and sees E.T. for the first time, Drew Barrymore was actually scared when E.T. suddenly stretched his neck up.
E.T. was voiced by the late voice actress Kazue Takahashi in the first dubbed version and the second dubbed version, he's voiced by both Ako Mayama and Rica Matsumoto at the same time (who, by sheer coincidence, they will reunite together again, except this time as enemies, as Aguila Setme and Lilcarla Borgnine respectively.
Throw It In: Gertie's line "I don't like his feet" was adlibbed, as was her "Give me a break" response to the claim that grown-ups can't see ET.
When Elliott yells "It was nothing like that, penis breath" Dee Wallace was supposed to angrily yell at him to sit down. When she actually heard him say the line, she starting laughing and they left that take in the movie.
Unintentional Period Piece: Averted nicely unlike a lot of 80s movies. You can tell it was filmed in the 1980s due to the cars, the TV, and the family owning an Atari 2600 but it doesn't stick out like other examples. Many of the pop culture references they make like Star Wars or The Twilight Zone are still known by today's audiences.
The first choice to play Gertie? Juliette Lewis. Her father made her turn down the role and Barrymore was cast instead.
Shelley Long was approached to play Elliot's mother. She turned it down as she was already signed on for the comedy Night Shift.
Stan Winston turned down the opportunity to work on E.T.. He would regret doing so.
The book "E.T. from Concept to Classic" features many plot points and scenes cut from the script. One subplot from an early draft was to have a rival to Elliott named Lance who wanted to expose E.T.. The spaceship was going to land in a parking lot, but it was changed to a forest because that sounded more magical, amongst many others.
There was almost a sequel where an evil group of E.T.'s people come to Earth looking for him and torture Elliott and his family for information.
Corey Feldman was originally up for a role as a rival to Elliott, a dork named Lance who threatened to expose E.T. The character is in the book adaptation, but was cut from the script. Steven Spielberg promised him a role in a future film, and he would go onto be in Gremlins.
Originally E.T. was going to develop a crush on Elliott's mother. Some scenes of this were filmed before it was scrapped. But it did make it into the novelization.
Word of God: Steven Spielberg stated that E.T.'s species is more similar to plants than any other creature and is genderless. Also, a series of trading cards from the 1980s list the family's last name as Taylor.