Not too long ago we had a monkey on board an F28. It was supposed to be a routine 'familiarization' flight for the animal, as it was training as a service animal. Instead shortly after takeoff the monkey literally went nuts, somehow got out of its leash/harness and raced around the cabin (full flight of course).
If that wasn't enough, monkeys apparently have the habit of urinating and defecating (sp) repeatedly when upset!
Can't remember if the plane returned or if they managed to confine the animal.
"The two most common elements in the universe are Hydrogen and stupidity"