Looking for an art book I found that the "painting in oils" jacket covered a "learning to use watercolors" book. When I approached a clerk I was met with an apprahensive glare. When she saw the nature of the mix-up she laughed, saying the usual problem was a deliberate re-dressing by young browsers, who loved watching the shocked reactions of sober readers finding sex manuals in the jackets of bird-watching guides or cookbooks.