Cedric has lice, which he picks out with his beak.[1][2] The Dungeon Cell is infested with mice, lice, and rats. Alexander could see fleas jumping furiously from cot to cot on the Pirate Ship. It is likely that lice had a cozy home there as well.
Rosella could have traded a strange, enchanted, weird device for a jar of lice from the Kangaroo Rat.