Continuity mistake: When Belushi and Ackroyd are sitting at the table having coffee, Earl throws his coffee at Ackroyd but if you play it in slow motion, you can see Ackroyd duck the coffee before Belushi actually throws it.
Other mistake: After Earl and Vic tangle in the swamp, Earl staggers back to his house to discreetly use the basement shower, where he is shocked to find Vic already there and waiting for him, hiding in the dark behind the shower curtain. Both men are literally covered from head to toe in thick, muddy muck from the swamp. but there is no trace of mud (handprints, smears, etc) on the shower curtain nor in the clean, white shower; and, when Earl manages to chase Vic out of the basement, he leans heavily on the door for a moment after slamming it, which should have left a huge, muddy print on the door's clean, white surface. But, as Earl steps away, there is no muddy print on the door at all. (00:38:57 - 00:39:42)