Cedric has lice, which he picks out with his beak. 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.