What would cause a ferret who doesn't usually chew to suddenly start chewing things?

Usually my ferret doesn't chew anything.. she gets a sock or something and she just hides it and thats it... but this morning I caught my girl chewing on a sock and she'd actually eaten a piece about 1 inch big.. no idea how long she'd be working on it.. and just not I caught her chewing on a bag!

I've had her for quite awhile, she's 2 years so she's certainly not teething... what else could cause this behaviour? A toothache, perhaps? Any other ideas?