Mine did that a lot when he was a baby/juvie. Always if he got too cold when he was out and also if he was annoyed. When he was shedding it happened more and also after I rearranged his cage decor. I thought he hurt his tail and it was tail rot at first, and totally got paranoid being my first reptile pet. It is something I have since seen in a couple other beardies. No need to worry it even lasted up to 48 hours one time and then went away.