A cowboy riding a bucking horse.
A man on a horse.
Just because it says cowboy doesn't mean it is a man.
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_horse(x3) & of(x3,x4) & n_bucking(x4) & (x1 = x2) & n_cowboy(x1))
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_horse(x2) & n_man(x1))