When Warren goes to the bathroom to tend to his leg wound, the shower curtain is hanging up, despite the fact that Jesse pulled it down only moments before.
Just after the frontal nudity on the beach, the girl lies down on the "one" chair available. When the camera pans across from the flies' perspective, there are three chairs.
When first introduced to the killer bugs it is daytime, the flies seem to have no problem with lights, or sunshine. Then later in the movie, the light incinerates them inexplicably as does the song, "Da Da Da".