Episode 52 of "Buffy, the Vampire Slayer"
s03e18 Earshot
Title: Earshot
Original Air Date: 09/21/1999 on WB
Director: Regis Kimble
Writer: Jane Espenson
Guest Stars: Ethan Erickson (Percy), Wendy Worthington (Lunch Lady), Robert Arce (Mr. Beach), Molly Bryant (Ms. Murray), Rich Muller (Student), Jay Michael Ferguson (Student), Keram Malicki-Sanchez (Freddy Iverson), Lauren E. Roman (Nancy Doyle)
Plot Outline:
After a close encounter with a mouthless demon Buffy is infected with the demon's blood and she gains the ability to hear people's thoughts. Her new found ability at first is good for cheating on schoolwork, but when the voices continue to flood her mind, she realises that she cannot control the power. While the gang tries to track down a would-be killer at the school, Buffy is slowly going crazy from the inability to block the noise from the minds of the people around her.