A man is watching something in the sky.
A man is looking at birds flying.
There are many things other than birds that a man could be watching in the sky, such as clouds, aircraft, etc.
exists e1 x1 x2 x3.(n_sky(x3) & Theme(e1,x2) & Actor(e1,x1) & v_watch(e1) & in(x2,x3) & n_thing(x2) & n_man(x1))
exists e1 e2 x1 x2 x3.(at(e1,x2) & Actor(e2,x3) & v_fly(e2) & (x2 = x3) & n_bird(x2) & Actor(e1,x1) & v_look(e1) & n_man(x1))