If you pray while there are hostile monsters near you, your god may decide to answer the prayer by frying all the monsters around you with lightning (sparing pets and peacefuls). This would work best when there are a bunch of hostiles right near you but none a medium distance away. Possibly it should be suppressed when your HP is low, but then again restoring your health while leaving you surrounded by monsters often doesn’t give you high odds of surviving.

The hero is not credited with killing the monsters, and gains no experience or penalties.