Blore shorts out the generator, killing all power in the ski resort. However, when the murderer is revealed, the light above the snooker table is on.
When Mike Raven (Fabian) is playing the piano, his bow tie is untied. However, when the others are examining the record player, he is shown pacing in the background with his bow tie tied. In the next shot, it is untied again.
When Herr Grohmann is preparing to go down the mountain on a rope, his gloves appear and disappear between shots.
The killer is shown playing snooker, but just before the credits roll, the stand with the ten indians is on the snooker table, making the game impossible.
When Shirley Eaton dresses for dinner her underwear is white (as noted in another goof). She then puts on a dress before opening the door for Hugh O'Brien. Later in the movie, when she is locked in her room, she is seen undressing and wearing black underwear. This is not a goof or continuity error. This is the next day and she has obviously changed clothes. She is no longer wearing a dress, but a skirt and sweater.
Obvious lights embedded in the sides of candles facing away from the camera - far too much steady light is on the characters holding the candlesticks than could be provided by a small, flickering candle flame. (Nice substitute for the usual follow spot.) And in a couple instances when Hugh is carrying such a candle, the power cord is visible coming from the base of the candlestick.
(at around 64 mins) A wire can be seen pulling a suit of armour supposedly falling down the stairs.
A large metal pin holding together Ann Clyde's bath towel is revealed behind her back by the reflection of movie lights, when she kisses Hugh Lombard and he carries her to bed.
The falling cable car is clearly empty, when it should contain a body.
During the course of the story, it is shown that the judge and the doctor share a bathroom, and that Lombard and Blore share one. Therefore, it is likely that Miss Clyde and Miss Bergen share one. When the other three survivors lock Miss Clyde in her room, however, no one suggests that they lock Miss Bergen's room, to keep Miss Clyde from escaping that way.
Why wouldn't the house guests just watch the tray with the indians to catch U. N. Owen as he/she breaks off the next one.