An open room lay before them, occupied only by a few cobwebs and dust. Upon entering, a phrase is seen on one wall. One of them utters the phrase out of wonder for its meaning, unknowingly activating the room. An eye opens on the wall in front of the poor souls and with a quick flash of light, the last thing heard from the room is heart retching screams... then silence.
Atheists and agnostics get a jolt when one or more deities make an appearance, and take a direct interest in things. It is hard to deny the existence of gods when one has met them face to face.