A white dog runs on the grass.
A white dog is chasing a squirrel.
Just because a dog is running, it doesn't mean that it is chasing a squirrel. Dogs run to play fetch, for fun, or to run away from something.
exists e1 s1 x1 x2.(n_grass(x2) & on(e1,x2) & Actor(e1,x1) & v_run(e1) & n_dog(x1) & a_white(s1) & Theme(s1,x1))
exists e1 s1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_chase(e1) & n_squirrel(x2) & n_dog(x1) & a_white(s1) & Theme(s1,x1))