There's a couple possibilities...
Maybe its jaw is out of alignment? Has it fallen or injured itself in any way?
Could be a sign of discomfort somewhere around the mouth. Mouth Rot? Loose teeth?
Could be respiratory infection. Look for excessive mucous in its mouth, listen for weezing or funny noises when it breathes.
Could just be one of those funny things our bps do on occasion apparently for no reason except to worry us!
In either case, pay close attention to your snake's behavior and make notes of other unusual things. Keep you husbandry tight, and look for signs of stress.