With her dark sensitivity, Imogen can make out that the tunnel seems strangely cramped. There's a great multitude of oddly shaped stalactites hanging down from the ceiling, hundreds of them. The whispering grows a little less vague and seems to be coming from something hiding amongst them.

Once the light floods the tunnel, though, the strange mystery is revealed.

Hundreds of angry Zubat hanging upside down screech to life at the influx of light! They flood forth like... bats out of hellish iron mines.

Good thing there's another tunnel to run down.