This falls in the stranger than fiction category.  A psychiatric patient admitted to my floor from a group home years ago with a recent diagnosis of incontinence.  His CAT scan revealed a calcified bladder stone formed around a sewing needle. When the stone filled the bladder completely, he developed incontinence, Unlike the typical patient who shows up with strange objects in strange places, he hadn’t absent-mindedly sat on it.  He gave an excellent history and remembered losing that pesky needle.  It just didn’t hurt, so he thought no more about it.