Meanwhile, Wolowitz and Koothrappali are pretty sure the government is out to get them when they are contacted about their guidance system.
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Sheldon's mother (Laurie Metcalf) also visits for the special occasion, as Penny tries to plan a wedding ceremony that will include all of their family and friends.
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We finally get to meet Leonard's dad! Judd Hirsch plays Leonard's dad, Alfred, who is recently divorced from Leonard's mother.
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We've seen what it was like to put Leonard's mother and Sheldon's mother in a room together, but what happens when you also add Leonard's dad to that mix? That's gotta be an awkward dinner conversation.
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Sheldon and Leonard's paretns have an awkward family visit on The Big Bang Theory. "The Convergence Convergence" is the 24th episode of the show's ninth season.
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Penny struggles to make a connection with Leonard's mother on The Big Bang Theory. "The Line Substitution Solution" is the 23rd episode of the show's ninth season.
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The gang heads out to a wine tasting on The Big Bang Theory. "The Fermentation Bifurcation" is the 22nd episode of the show's ninth season.
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A heated argument breaks out during a get-together on The Big Bang Theory. "The Viewing Party Combustion" is the 21st episode of the show's ninth season.
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Raj goes overboard with pregnancy gifts on The Big Bang Theory. "The Big Bear Precipitation" is the 20th episode of the show's ninth season.
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Koothrappali sells out Leonard and Wolowitz after they lie to their wives. "The Solder Excursion Diversion" is the 19th episode of the show's ninth season.
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The boys run into problems when they file for a patent on The Big Bang Theory. "The Application Deterioration" is the 18th episode of the show's ninth season.
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Sheldon gets a birthday surprise on The Big Bang Theory. "The Celebration Experimentation" is the 17th episode of the show's ninth season.
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TBBT Quotes

Sheldon: Why do people cry at weddings?
Mary: They're practicing for what's coming later.

Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.