Revealing mistake: When Bill Duke picks the scorpion off Carl Weathers' shoulder with a knife, you can blatantly see some gum or similar that's been used to stick the scorpion onto the tip of the knife. Even if it's meant to be Bill Duke's gum, it's not on the tip of the knife before he stabs it.
Suggested correction: It isn't gum, it's literally the scorpion's guts.
There are no guts in the scorpion's body, so it's obviously some material to stick scorpion to the tip of the knife, and it's blatantly visible in the close shot.
It's the abdominal fluid. It probably is gum in real life but if you kill an insect you will find it has a gum-like fluid in its abdomen.
Audio problem: When Anna hits Poncho and takes off running, Arnie "whistles" at Hawkins with his mouth closed and the camera is looking directly at him when it happens. (00:41:05)
Suggested correction: The whistle is a tongue whistle. The tongue is curved via the teeth and the lips need to be almost closed to make the air rush out in that manner. It's sharper than a regular whistle due to this.
Other mistake: When the Predator sees Billy on the log bridge, there is a cold blotch in the middle of Billy's chest. He's not wearing anything that would make such a hole in his heat signature - it should be the same color as the rest of his torso. It doesn't even match up with the cut he made across his chest; the cut starts much higher than the blotch and the blotch is irregularly shaped, not indicating the smooth line of a cut. (01:15:20)
Suggested correction: The cold area is the blood running from his wound. It is cooling down on contract with the air.
Character mistake: When Mac describes what he saw after Blaine was killed, he states that he "capped off 200 rounds with the minigun." At the rate the minigun fires, and the length of time Mac was shooting, he fired at least 10 times that amount. Perhaps he meant to say "capped off 2000 rounds." This adds to another mistake: the ammo pack Blaine carried only holds 500 rounds but much more than that is fired during the course of the film.
Suggested correction: He actually says "capped off 20 rounds, in the minigun...full pack" just the word spacing is a bit odd. 20 rounds refers to his normal gun which ran out of ammo quickly.
