And some babies will do this when they feel insecure. Make sure the tub/cage is situated in a quiet room and you are giving your baby enough time to settle in. Hide boxes are good for young boas. Boas are not generally as shy as BPs, but they do need to feel secure. You might even have to black out the sides and back of the enclosure.

I would avoid throwing a towel on him. He will begin to expect that and from the snake's point of view, that would be quite terrifying. Hook training is a much better way to help him overcome the fear and aggression.