In the casino scene after Willard bets on 7, the croupier spins the ball inexpertly and it can been seen to judder quickly to a stop on the roulette wheel. In the next, closer shot, it spins the rim rapidly before settling on 7.
(About 14 minutes in) Gwendoline is carrying the pair of nun-chucks she picked up in the back room when she ducks under the roulette table. The next scene shows her and Beth crawling under the table and the nun-chucks are nowhere to be seen.
During the fight scene on the river between Willard's boat and the Chinamen's Junk, one of the subtitles shows a character's line and then follows it with the word "Bible?" which has no relevance to anything on the screen and seems to refer back to a line at the start of the film.
Most of the dialogue is not lip-synched accurately.
Many of the closing-trap walls in the end sequence can be seen to stop just shy of the lens while the grinding-stone sound effects continue.
D'Arcy makes many references to unleashing the power of "The Volcano." No volcano is ever seen in this desert-by-a-jungle-by-a-river called the Yek Yeuk.