Nursery rhymes can be nightmares, too. Or, at the very least, a reminder that fantasy can be just as gloomy as reality. Under the weirdly mischievous name Let's Eat Grandma, Jenny Hollingworth and Rosa Walton make music that runs around the notions of pop — it is, at turns, unsettling, joyous and experimental. So, of course, we asked them to sing us to sleep.