Steve,
The reason I say that they probably aren't plastic model parts is that old prop builder's addage: "Never trust an actor with your prop!"
Having built my fair share of props for movies and television, I would have had a hard time justifying using a fragile plastic model bit as the whiskers on Muffit 2 because I would have immediately suspected it to break off under the delicate ministrations of Eve the chimp or her stunt double.
But you never know. Might have been a bad decision day in the prop department and they got REALLY lucky over the run of the show and the intervening years that they never broke off. However, I would also hasten to point out that the piece bridging the eyes to the muzzle is a 3 penny nail, so sombody was thinking about how sturdy this thing was to some degree.
Just my observations.
-G