(at around 56 mins) Benson strikes Adam on the head with a lamp. It leaves a bloody gash that comes and goes during the ensuing chase scene.
When Adam is going to leave Benson 'to the robot', he's about to close the door when it cuts back to Benson pleading on the table. Adam's hand can be seen helping him, even though at that point, he's over at the door saying he won't leave him. Time 36:46.
When Adam jumps into the wastewater with Hector, it is clearly a stuntman wearing a bad wig.
In the final scene, where the ship flies toward Earth, the space background with stars is visible through the ship.
When Benson gets his hand cut off by Hector, for a brief moment, his hand is still attached when he's dropped by the robot.
The robots reattaching Hector's arms is really his arms being pulled off, shown in reverse.
Much of the dialogue is clearly ADR. Several times characters are speaking without their mouths moving.
When Adam (Kirk Douglas) picks up one of the "Blue Dreamer" pills off of the dresser in the bedroom, a crew member can be seen moving in the lower corner of the mirror in which Adam's reflection is visible.
(at around 5 mins) Visible wires that lift Captain James off the floor when Benson murders him.