The boys are quickly embroiled in a messy gun battle with dozens of inept aliens and Ozzy couldn't be happier. Derek pulls himself together and jury rigs a couple of ways to keep his head together before embarking on a chainsaw rampage. Poor schmucks, it is too late when the leader realizes he has a Derek on board. People carrying axes are rarely friendly. Sledgehammers are laying around all over the place in New Zealand.
Brains are spoon food.
When your skull is cracked and brains are falling out avoid tight hats. Blood is slick stuff, mop it up before someone gets killed. Vomit is delicious. Pine cones are about the least threatening thing you can chuck at someone who has a chainsaw. Kicking a decapitated torso in the balls accomplishes very little.