Get your eye-covering blankets and scream-muffling pillows ready. The most terrifying show on TV is back for a third season tonight. Check out American Horror Story: Coven on Eleven at 9:30pm and be prepared to want to/actually sleep in your parents' bed (yep, just like the first time you watched The Exorcist). Missed the first two seasons of AHS? Here's what you need to know.