Alligator
"It lives 50 feet beneath the city. It's 36 feet long. It weighs 2,000 pounds...And it's about to break out!"
A baby alligator is flushed down a toilet and survives by eating discarded lab animals that have been injected with growth hormones. The now gigantic animal escapes the city sewers and goes on a rampage, pursued by a cop and a big-game hunter.