Make every item have a random chance of being a mimic that’s been paralyzed or bound into service as an item. Keep track and wait for the party to remove a curse from party members carrying one or to inadvertently complete the bound mimic’s service.
Like a potion of healing, but it’s always screaming. The screams cannot be heard when the potion is contained (say, in a bottle or in someone’s stomach). However, once the potion enters the drinker’s blood stream, their blood will also begin to scream. This goes unnoticed until the drinker gets wounded.
