You aren't quite sure what you've tripped on in the darkness, your flashlight having gone off long before, but you know what you've tripped into, as you get a mouthful of goo. You gag and try to push yourself away, but more falls onto your back, spreading onto your shorts. You stumble again as the goo almost seems to yank at you, covering your head with your arms.
The vents feel cold, but the slime is making you feel hot, melting away your human body and changing it to something much better suited for these tunnels. You cry out when a second pair of limbs burst from your sides, gripping onto the stone as your legs become animalistic. You pant, a new eye sprouting with every blink as the goo on your backside forms into a heavy abdomen.
With a shower of goo, the slime shifts to a mixture of chitin and fur, and you pant, trying to regain your composure. At least it doesn't feel so cold anymore...