What's the deal with the scalpels? I know they get bigger as the fish gets bigger, but are they more pronounced for any reason?

The reason I ask is that my yellow tang (about 5.5-6 in.) and my yellow eye kole tang (about 4.5-5 in) suddenly have their scalpels "protruding" almost all the time. They didn't used to be like that. I noticed the change about a week or so ago.

On one hand, one might think it's a good thing and that they are just very healthy. On the other hand, though, maybe it's a sign that they are not in good shape and they are trying to protect themselves. They both look good, though.

On a side note, they never fight with each other or bother any of the other fish. In fact, they usually go and hide when I walk into the room. But, when I sit down to watch them, they come right back out. The yellow eye likes to swim like a maniac from one end of the tank to the other. He takes off from one end and then just change directions and go the other way or dart behind some rocks.