The bird's feet are grasping the window tightly.
The bird has it's feet on the window.
The bird is grasping the window a window using his feet, his feet therefore have to be touching the window.
exists e1 s1 x1 x2 x3.(n_window(x3) & n_foot(x2) & of(x2,x1) & n_bird(x1) & a_tightly(s1) & Manner(e1,s1) & Theme(e1,x3) & Actor(e1,x2) & v_grasp(e1))
exists e1 p1 x1 x2 x4.(n_window(x4) & n_thing(x1) & n_bird(x1) & exists x3.((x1 = x3) & on(x3,x4) & n_foot(x3)) & Theme(e1,x1) & Actor(e1,x2) & v_have(e1) & (x1 = x2))