Season 9, Episode 2 - The Separation Oscillation
Aired September 28, 2015
As Leonard and Penny struggle with the revelation he kissed another woman, Leonard goes to meet the woman in question, Mandy, in a bid to show Penny there's nothing to worry about. Elsewhere, Sheldon films an episode of Fun with Flags alone following his break-up with Amy, who is angered by Sheldon's thinly veiled comments about their recent split.
Meanwhile, Bernadette is uncomfortable with the fact she's known about Leonard's kiss for two years after Howard told her, while Raj is unhappy that he did not share the gossip with him.
Season 11, Episode 13 - The Solo Oscillation
Aired January 11, 2018
After Sheldon decides to work solo without Amy, she turns to Leonard to work together on a series of science experiments. Meanwhile, geologist Bert replaces Howard in Footprints on the Moon, while Sheldon gets an unexpected source of scientific inspiration from Penny.