After Beverly's squash game, as the twins discuss their research, a compositing error causes Elliot to become translucent as he walks off screen. A similar oversight causes his shadow to vanish earlier in the same scene.
In a scene dated 1954, the twins seen are playing with The Visible Woman, Revell toy company's biological model of a woman that was not marketed until at least five years later.
Jeremy Irons used his British accent to play the roles of the adult twins, even though the characters grew up in Canada.