You wait for the acid. Strangely, it never comes. Instead, The panel rises up and locks into a hole in a larger panel. This time, there are railings on the edges of the panel which you would have fallen off of on the smaller panel. You can go F(orward), R(ight), L(eft), B(ack). There is the REVOLVER, the RIFLE, and the SHORTSWORD on the ground.