People standing in mud.
There is mud and people are in it.
People standing in mud is a rephrasing of there is mud and people are in it.
exists e1 x1 x2 x3.(a_topic(x1) & in(e1,x3) & n_mud(x3) & Actor(e1,x2) & v_stand(e1) & (x1 = x2) & n_people(x1))
exists p1 p2 x1 x2 x4.(n_thing(x4) & in(x2,x4) & n_people(x2) & exists x3.((x1 = x3) & n_mud(x3)))