TB moments...Lester had a few last week. A "TB moment" is the act of when a horse "checks out" of their own mind and freaks out/ spooks over "nothing". The "nothing" can be anything from a ferocious squirrel to an unmoving object like a plastic bag (OK, ok they are a bit scary when they do in fact "move"), rock, newly painted fence, etc.
The pic you see to your left has captured a TB moment. He's spooking at the trees. Gotta love him.