The bird's feet are grasping the window tightly.
The bird is sitting on the window
If the bird's feet are grasping the window, the bird is sitting on 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 x1 x2.(n_window(x2) & n_bird(x1) & on(e1,x2) & Actor(e1,x1) & v_sit(e1))