What's that Sound?

"What's that sound?" Matt asked and spun around, the light from his flashlight casting long shadows on the tunnel walls.
   "I... I don't know," Quinn replied, also shining his flashlight up and down the passages. There wasn't anything in sight, but there was a series of squeaks coming from down both sides.
   "Rats?" Matt asked, then more affirmatively he said, "They must be rats."
   Suddenly they heard a scream from down one of the tunnels. It lasted for a minute, then was abruptly cut off, replaced by shrill, squeaking sounds.
   "That must have been Dana," Matt said.
   Quinn was about to call for her, but didn't have to. From around the corner, floating on the water, was a body. It was wriggling though, and when Quinn shone his flashlight, he saw rats, covering it.
   They all froze and turned their heads simultaneously to look at him. Then as one they began to hiss, the noise sounding like a group of demonic cats. Their eyes burned red in the darkness.
    "This can't be. They're just rats."
    "Just rats..." Matt echoed
     Then the things that were rats but weren't just rats, slowly slipped off the body and surged towards them like a wave.