Go to the part where Burt and Heather are blowing away the Grapoid that breaks into their basement. After Heather free's Burt from the Grapoid's tongue he gets back up and starts shooting. When he does look behind him. A handgun hanging on the wall behind him falls and when the scene cuts away and then cuts back the gun is back on the hooks. Kinda weird they would purposefully put the gun back up on the wall.