Other mistake: When they raise the temperature of the room with the facehuggers in, once the room is at body temperature, they open the door onto the much colder corridor. This would have immediately dropped the temp in the facehuggers' room.
Other mistake: Irs stabbed Richard completely through his face and shot him in the torso. Although he fell in the lake, he is later shown on the shore and he is not bleeding. Head wounds normally bleed like crazy. Since he is wounded in two places, he should have drowned or bled out from swimming to shore. (01:19:51 - 01:25:08)