Sharks Don't Swim Backwards
Sharks can't swim backwards. It's impossible. Their fins are not flexible like other fish. They can only go backwards by stopping and falling backwards. However, the shark in the movie backs out of a vent pipe, and it's stated that it used the pipe as a hiding spot. There's no way it could get in and out.
How Many People Did it Eat?
The shark eats Simon McCorkindale's character. It then swims around a bit and attacks a dolphin. Then a few minutes later it attacks the undersea control room and eats at least one technician. Yet, McCorkindale's character is still just inside the shark's mouth, and is even still got his right hand extended with the grenade in it.
