This is a small whistle. It appears to be made of rowan wood.
The wooden whistle is a wind instrument, requiring the crafts.music.instruments.wind skill to play. A bonus of approximately 150 in this skill is required to play with average ability. Apart from the usual commands for musical instruments, you can "blow" a whistle.
Whistles and fruitbats
cast Granny Benedict's Bond of Loyalty with whistle for <fruitbat>. Once this has been done, the fruitbat will return from any nearby room to the witch's location when the whistle is blown.