A mountain skier heads down a mountain.
A skier is falling down a mountain.
heads down and falling down are different activities
exists e1 s1 x1 x2 x3.(a_down(s1) & Manner(e1,s1) & Theme(e1,x3) & Actor(e1,x1) & v_head(e1) & n_mountain(x3) & n_skier(x1) & of(x1,x2) & n_mountain(x2))
exists e1 s1 x1 x2.(a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_fall(e1) & n_mountain(x2) & n_skier(x1))