While there are more than 15,000 museums in our country, visitors get to see only about five percent of any institution's collections. Most museums simply don't have room to display everything they've got. However, there are a wide variety of surprising and intriguing reasons that, for example, the Smithsonian Institution doesn't display its collection of condoms, Florida's Lightner Museum locks up all but one of its shrunken heads, and a world-class...