There's nothing on the ceiling just yet, thankfully. And the headcrabs are screaming with animal rage to a degree that might block out the death noises. The spidery-legged ones present the most problems; they're faster than the black ones or the ones that look like bloated ticks, and they leap without warning. Gordon is mostly firing at them as they flee through the twisty tunnels.

It's not until they come to a gap too wide for a human to jump that this becomes a problem. Gordon looks as if he'd like to swear at the sight, but says nothing; instead he peers over the edge. "Water," he says tersely. "It's got a current- it's flowing somewhere. And I think I see light in the distance. Can you swim?"