That does n't look like mud on the horse rider.
The substance on the horse rider is brown in color.
just because it doesn't look like mud doesn't mean its not brown in color.
exists x1 x3 x4.(n_rider(x3) & of(x3,x4) & n_horse(x4) & n_thing(x1) & -exists e1 x2.(like(e1,x2) & on(x2,x3) & n_mud(x2) & Actor(e1,x1) & v_look(e1)))
exists e1 x1 x2 x3 x4.(n_rider(x2) & of(x2,x3) & n_horse(x3) & n_substance(x1) & in(e1,x4) & n_color(x4) & Theme(e1,x1) & v_brown(e1) & on(x1,x2))