Legend has it that writer Sylvia Wright misheard the lyrics to "The Bonny Earl of Murray" when she was a child. The actual lyrics are "Thou have slain the Earl of Murray and laid him on the green", but what she heard was "Thou have slain the Earl of Murray and Lady Mondegreen". And the mondegreen was born.
Fortunately, these aren't limited to songs ("'Scuse me while I kiss this guy"). Medical mondegreens abound. Some like Old Timers' Disease (Alzheimer's) are quite descriptive, but wrong nonetheless.
Yesterday a patient told me that his legs always swelled because of his very close veins (varicose veins).
Another patient came to my office complaining of pain at her biblical hernia (umbilical). Fortunately the fireballs in her eucharist (fibroids in her uterus) didn't bother her.
Some are a bit harder to decipher. It took me a good 5 minutes to figure out that the lady with "65 roses" actually had cystic fibrosis. And the little girl with Smilin' Mighty Jesus really was suffering from spinal meningitis.