This will make you laugh, those of you who have slow cookers.
A relative of mine was baby sitting for her daughter for the day and decided to make a casserole in the daughters slow cooker as a nice surprise for when she came home.
She prepared the casserole and put the ingredients in the ceramic pot , then she poured water into the metal heating pot, thinking she'd seen her daughter do the same thing. She switched it on and left it for the day. Fortunately, all that happened was that the outer pot became horribly stained. I think she was luck not to have killed herself!