A zebra is nibbling on some grass.
A large creature is standing in grass.
A zebra can nibble on grass without standing.
exists e1 x1 x2.(on(e1,x2) & n_grass(x2) & Actor(e1,x1) & v_nibble(e1) & n_zebra(x1))
exists e1 s1 x1 x2.(in(e1,x2) & n_grass(x2) & Actor(e1,x1) & v_stand(e1) & n_creature(x1) & a_large(s1) & Theme(s1,x1))