Whenever they glance over: the wing is gone, leaving only a sticky trace of blood on the floor.

As they move forward, for a time, there's nothing. No noises, no lights . . . nothing but the length of the tunnel. Whether they move slowly or quickly, it won't matter: there doesn't seem to be any end to them. And are the walls getting closer? It's hard to tell, but after a while, they'll begin to notice the tunnel is getting narrower and narrower.

It continues that way until their arms are uncomfortably pressed against their sides, until the air seems a little too thin, until there's just a railway line despite the fact no cart could come through here--

And then they face a choice. The tunnel splits: left or right?