That's one of the dangers of allowing the beak to become overgrown. Just like when you have an extra long fingernail and you bump it on something and it breaks. Same thing happens with an over long beak. It will eventually snap off...and usually a bit shorter than is comfortable for the tortoise. So, take a nail clipper and finish trimming the edge of that beak, or take him to the vet and have a vet trim it for you.