The Return of the Living Dead (1985)

Morgue attendant Frank tells Freddy, the new guy on the job, that the story of ‘Night of the Living Dead’ was a fictionalization of events that actually happened and shows him a canister of the military gas that supposedly caused the dead to revive. Hitting the canister to show how secure it is, he succeeds in rupturing it and the gas spreads throughout the morgue re-animating several exhibits and a dead body. But as the body comes after them they find they cannot kill it, even when they cut it to pieces, so they cremate it. But rain washes the ashes down into the neigbouring cemetery, re-animating all the bodies there.