cackle-bladder

noun1

1. •
   A bladder containing (real or fake) blood, used to fake someone's death or injury, as in espionage or confidence tricks where a person is made to think that he is an accessory to murder.

   • Use a cackle bladder to bite on and spit blood whether faced with a gang or a single assailant. This is often enough to dissuade would-be aggressors […]. — 1975