According to kinkpedia – here is what nosehooks are all about:

Nose hooks are the smallest variant of bondage hooks.
Nose hooks come in two variants. The more common variant, usually used in japanese bondage, is a small two prong hook. Each end of the hook is inserted into one nostril while the middle of the hook is connected to a head harness This pulls the nose up, creating what is often refered to as a pig nose look.
The second variant is fairly uncommon. It consists of two separate hooks, one in each nostril, that are pulled sideways by little strings running across the wearers cheeks.