- The continuing repercussions of an action.
- A sound that is prolonged by repeated echoes.
Season 8, Episode 4 - The Hook-Up Reverberation
Aired October 6, 2014
Raj's openness about his romantic history, including his inadvertent hook-up with Penny, leads to tension when Emily finally meets Penny. After Emily is frosty to Penny, Raj tries to patch things up.
Meanwhile, the guys consider investing in Stuart's comic book store to help it reopen after the fire, although the women in their lives don't see the investment potential.
Season 9, Episode 10 - The Earworm Reverberation
Aired December 10, 2015
Sheldon has a revelation when he realizes why a song was stuck in his head. Also, Amy invites Dave over for dinner despite their previously awkward date, and Wolowitz and Koothrappali become obsessed with a fan of their band, "Footprints on the Moon".
Season 10, Episode 15 - The Locomotion Reverberation
Aired February 9, 2017
When Sheldon proves to be a distraction to Leonard and Howard as they work on the military project, they find a way to keep him occupied but his absence threatens to derail the project after Colonel Williams demands the gyroscope be made smaller.
Meanwhile, Penny and Amy take Bernadette on her first girls' night out since Halley was born, leaving Raj and Stuart to look after the baby.
Season 11, Episode 11 - The Celebration Reverberation
Aired December 14, 2017
As Sheldon plans a birthday celebration for Amy, Howard is looking forward to Halley's first birthday. Meanwhile, Leonard has the holiday blues when he receives a Christmas letter from his brother detailing his many accomplishments.