A dog chews on a stick.
A dog is chewing a wooden stick.
The stick doesn't have to be wooden.
exists e1 x1 x2.(on(e1,x2) & n_stick(x2) & Actor(e1,x1) & v_chew(e1) & n_dog(x1))
exists e1 s1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_chew(e1) & n_stick(x2) & a_wooden(s1) & Theme(s1,x2) & n_dog(x1))