How about a real hiss
When I was first learning to fly bugsmashers in the late 1970s, my instructor told me that he once had to take a hessian bag of brown snakes (the deadly variety) from one aerodrome back to Canberra for the wildlife service.
He suddenly realised on approach that the bag had opened and the snakes were on the floor in the rear of the PA28. He didn't declare an emegency but I understand his approach and vacation of the runway was expedited.