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'The Maternal Combustion' - Season 8, Episode 23
When Sheldon and Leonard receive an award for the paper they co-wrote together, their mothers pay a visit to Pasadena. Sparks fly between Mary Cooper and Beverly Hofstadter when they can't see eye to eye on religion or psychiatry. Meanwhile, Bernadette has had enough of feeling like a mother to three teenage boys, so Howard, Stuart and Raj are ordered to clean the kitchen.
Air Date: April 30, 2015.