"The Lion Sleeps Tonight" is the eighteenth episode of the eighth season of Grey's Anatomy and the 166th produced episode of the series. It is also the 259th produced episode of the Grey's Anatomy franchise. It was broadcast on April 5, 2012.
After Meredith and Derek encounter a lion roaming the streets of Seattle, a flurry of victims of the animals rampage arrive at the hospital, including its owner. Owen tries to make up for his indiscretion against Cristina by going through Meredith while Lexie turns to Derek for advice when she learns that Mark is planning on asking Julia to move in with him. Callie quizzes Arizona on her romantic history and the plight of Teddy's patient forces her to come to terms with her status as a widow.
- "We have a saying in the operating room, 'don't pet the lion'. It means no matter how nice a tumour looks, now small it is, how perfect it's margains may be, it's still a tumour, it's still dangerous and it can bite."
- "We've all heard the warnings and we've ignored them. We push our luck, we roll the dice. It's human nature; when we're told not to touch something we usually do even if we know better maybe because, deep down, we're just asking for trouble."
- "What Have I Done" - Anna Ternheim
- "Wax" - Theme Park
- "Are You Sleeping" - Winterpills
- "Amongster" - POLIÇA
- "The Weight Of Love" - Snow Patrol
This episode's title originated from the song The Lion Sleeps Tonight, originally sung by The Tokens.