This is a discussion on What is this horse doing this for??? within the Horse Videos forums, part of the Horse Pictures, Videos, Artwork, and Contests category
Probably because he is bored. However, it looks like he is biting his tongue pretty hard. If so, he may be forcing an endorphin release....kinda getting a high from it. The same result horses get from cribbing.
Probably because he's bored, or like Allison mentioned he may be getting an endorphin release from it.
I find it rather amusing, but if it became an issue where the horse was putting its health at risk I'd probably try to find a way to keep the horse amused. Plenty of hay, toys in the stall or in the paddock, a pet goat...