After the hooks are in Pat's breasts, they are twice as long as they were before.
(at around 28 mins) When the group arrives at the village, the corpse of the Portuguese is decomposed far more than it would normally be after one day, even in the rain forest. Also, other people who died before him weren't decomposed at all.
Rudy wears a neckerchief bearing the OshKosh logo, but the lettering seems to switch between being a 'mirror image' of itself (so it reads hsoKhsO) and appearing as it should, often several times within one scene.
After Mike's hand is cut off, his arm is bandaged up, but it's longer than it was with his hand still attached.
When native hunter stabs dead Joe with a spear, he is clearly just painting him with fake blood.
First 2 victims found in the jungle are both clearly alive when characters find them because their breathing can be seen, yet they act as if they are dead.
Dead man laying in front of the shack clearly breathing when they first enter the village..
(at around 37 mins) When Mike and Rudy get into a fistfight, twice Mike pulls his gun and you can hear the sound of the hammer being cocked. Both times, you can see the gun and the hammer is clearly down.
(at around 3 mins) When the man at the beginning of the movie is shot, the bad guy attaches a silencer onto the gun, but you can hear a very loud bang when the trigger is pulled.
When handed a watch by a tribesman, Myrna turns it over and says she had Mike's initials engraved on it. 'Mike Logan' appears in full, not just as initials.