This full cheek jointed snaffle has copper keys hanging from the center of the mouthpiece. This type of bit is used on young horse in the early stages of their training. The copper keys give the young horse something to play with, and letting him get used to the feel of the bit in his mouth and increasing salivation.
The Bit Gallery - Snaffle bit with Whistle Mouthpiece
Description and uses of the whistle snaffle.