Graphic 92, a head, is deadly (MAKE_DEADLY) and enters here; graphic 87, a block, enters at PACER_U. Either moves two units a turn along U, the way bit 0 of +10 says (set: forwards), and turns round when it bumps into anything. It never falls. The player standing on the block is carried along, since the collision code gives him the step of what he stands on when he has none of his own (ADJ_DZ_FOR_OBJ_INTERSECT).