Continuity mistake: When Alice returns to the caterpillar and he says "keep your temper" he is coloured opposite to how he normally looks, with a dark blue front and light blue back. (00:34:15)
Revealing mistake: The Thing takes a swing at the captain after the captain opens the door. As the Thing swings his arm, he takes out a chunk of wood out of the door. If you step through the frames on the DVD, you can see the wood leaving the door a full second after the Thing has hit it. A small explosive charge that was not in sync with the actor. You can also see the outline of where the wood comes off before he swings his arm. And one more thing, his arm does not touch the door or even comes close to where the wood comes off - a safety precaution I presume. (00:57:33)
Suggested correction: It is not a full second delay. It is four frames which translates to 1/6 of a second. Everything described in this entry is only visible if you step through frame by frame which invalidates the mistake.
Visible crew/equipment: When Gort picks up Patricia Neal next to the flying saucer, you can see cables leading down to her body to keep her hoisted. (01:20:15)
Continuity mistake: When Sylvester is banging on the door of his apartment, there is no handle on the door. When his lady opens the door, a handle has appeared, and the door panels change.
Continuity mistake: After crossing the first rapids, Humphrey Bogart's shirt appears to be mostly wet in the back. When he talks to Miss Sayer, it's the front of it soaking wet. (00:39:15)