6. Lisa Fails At Babysitting - "My Sister, My Sitter" (8.7)
This might not be shocking in the same way that some of the other moments listed here are, but it's weird and scary in its own way. Season seven's "My Sister, My Sister" poised Lisa as Bart's babysitter, but she ultimately fails and Bart ends up with a dislocated shoulder, unconscious in a wheelbarrow, in a muddy trench. It's the stuff of nightmares - and given the nature of Bart's injury, it felt a bit too realistic for comfort.