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.
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.
The first choice to play Gertie? Juliette Lewis. Her father made her turn down the role and Barrymore was cast instead.
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.