Four birds are chasing another bird which has a piece of food in its mouth
the birds are trying to get the food
We can not assume that there was a  birds that had a piece of food in it's mouth.
exists e2 e1 x1 x2 x3 x4 x5 x6.(Theme(e2,x2) & Actor(e2,x1) & v_chase(e2) & Theme(e1,x4) & Actor(e1,x3) & v_have(e1) & in(x4,x6) & n_mouth(x6) & of(x6,x1) & n_thing(x1) & of(x4,x5) & n_food(x5) & n_piece(x4) & (x2 = x3) & n_bird(x2) & -(x2 = x1) & n_bird(x1) & n_bird(x1) & card_eq_4(x1))
exists e1 p1 x1 x2.(n_food(x2) & n_bird(x1) & Topic(e1,p1) & Actor(e1,x1) & v_try(e1) & exists e2.(Theme(e2,x2) & Actor(e2,x1) & v_get(e2)))