Continuity mistake: In the scene where Jonathan picks up the scarab, it breaks open and the beetle inside starts to crawl under his skin. We see Brendan Fraser tear Jonathan's shirt and cut the beetle out of him. However, in the very next scene, we see Jonathan walking into the temple, his shirt is intact and there is no blood to be seen. (01:37:05 - 01:38:30)
Visible crew/equipment: In a scene in a cave that is the lair of the "eaters of the dead," the camera takes an overhead wide angle shot of the "eaters" walking down into the cave. It is possible to see a young man wearing a burgundy t-shirt and beige shorts (a crew member), sitting against the wall of the cave cross-legged.
Deliberate mistake: When Tarzan fights with the leopard, it scratches his chest. However after they fall into the pit and Tarzan comes out carrying the dead leopard, the scratches on his chest have amazingly healed. [It is a long-standing Disney tradition that no evidence of violence is shown on screen. Still a mistake, but there's why].
Continuity mistake: When Silent Bob renders the demon disabled by using the anti-odour spray, you see him take the spray out of his coat and spray with his thumb. However, it cuts to a front view, and he is clearly seen using his index finger. It then cuts to Bob's rear, and he is, again, spraying with his thumb.
Continuity mistake: In one scene, Liv Tyler's character informs another character that they suffer from halitosis. The film is set in the 1700's, and the condition of halitosis was invented in the 1930's as a method of selling fragrances and deoderants. Therefore, the condition she refers to doesn't even exist at that time.