Tin whistle
A small pig-shaped tin object with a whistle in its tail, found in the Nome King's palace, containing an enchanted Tin Woodman.
First named in Ozma of Oz, ch. 19
a curious tin whistle from his pocket
As the books describe them
It was in the shape of a little fat pig, made of tin and painted green. The whistle was in the tail of the pig. Ozma of Oz, ch. 19