Visible crew/equipment: In the lower left-hand pane of glass in the kitchen cupboards, a crew member can be seen moving a rat (Ben) from the center table to where Willard left the box of rat poison. (01:30:42)
Continuity mistake: When Willard goes to confront his boss, Al Martin, about killing Socrates earlier that day, we get a good view all around Al Martin's office. There are a few rats on the desk, coffee table and a chair; but there are absolutely no rats climbing the curtains. Al Martin realises Willard is insane and they struggle briefly, whereupon a single rat leaps on Martin's arm and bites him as he screams. In that moment, seven rats suddenly appear climbing high up on the curtains behind Al Martin. The camera makes a one-second cut to Willard for his famous line, "Tear him up!" The camera immediately cuts back to Al Martin, and now all the rats have disappeared from the curtains in the background.
