The genius was in the packaging. Each Pet Rock came in a cardboard carrying case, complete with air holes, tenderly nestled on a bed of excelsior. Mr. Dahl's droll masterstroke was his accompanying manual on the care, feeding and house training of Pet Rocks.

"If, when you remove the rock from its box it appears to be excited, place it on some old newspapers," the manual read. "The rock will know what the paper is for and will require no further instruction. It will remain on the paper until you remove it."

Pet Rocks hit the marketplace in time for Christmas 1975. They were soon featured on The Tonight Show and in a blizzard of newspaper articles. In a matter of months, some 1.5 million rocks were sold.