Oh....another time, we hid prawn (shrimp) shells in different places in our Boss's office.
In the back of his cabinet, under files, in the telephone, even in the light fitting in his office, oh and someone, even unscrewed his office chair and put some down the tube under the chair.
He found most of them, but the one in the chair had him baffled for a while.
Good thing he had a sense of humour, as his office stunk for days.