THOUSANDS of years later, we can view stone-age art on cave walls, but we can't listen to the stone-age music that would have accompanied many of the pictures. In many sites, flutes made of bone are to be found nearby. Iegor Reznikoff of the University of Paris reports that the most acoustically resonant place in a cave " where sounds linger or reverberate the most " was also often the place where the pictures were densest. And when the most-resonant spot was located in a very narrow passageway too difficult for painting, red marks are often found, as if the resonance maximum had to be signified in some way. This correlation of paintings and music, Reznikoff says, provides "the best evidence for the ritualistic meanings of the paintings and of the use of the adorned caves." Proceeding into the direction of the best resonance (or echo) that answers to vocal sounds, one is naturally lead to panels with pictures. At the very least, in the dark caves, where hand-held light sources fall off in effectiveness, singing (and listening for resonant reactions) proved to be the best sonar-like way of exploring the caves. A significant returning sound gave some hint of a usable hall ahead in the dark. On the 5th and 6th of July, Reznikoff will conduct a tour of a prehistoric cave where he will show some examples of the sound-picture relationship. He will also lead a visit to the Basilica of Vezelay where he will illustrate the magnificent resonance. (Talk 4pAAa1, " Sound resonance in prehistoric times: A study of Paleolithic painted caves and rocks" was presented July 3, 2008.)