At minute 14:45, one of the toxic waste dumpers closes the tailgate on the pickup truck without placing the hooks in the latch mechanism. As the truck drives off, the hooks are shown in the latches.
Assuming that the 55 gallon barrels shown at the start of the movie are half full of nasty chemicals they would weigh over 200 pounds and would be impossible to be causally lifted by one person.
No power source for the lab equipment that the Professor has. The equipment shown requires electric to work.
When Elizabeth faints after seeing the monster, the professor crouches over to see how she is. He must have felt the heat from the campfire on his backside, because there is a jump in the film and he is now repositioned away from the fire.
At minute 02:30, when the barrels are being dumped in the lake, the barrel is fully horizontal before any liquid begins running out. It is a liquid, not a sludge as stated by the gent carrying the barrel to the lake.
During the "song" sequence, Proffessor Jackson stops playing the guitar briefly despite the music continuing. The back up singers being heard are also a give away to his lip-syncing the song.