Think you know everything about The Big Bang Theory?

The popular sitcom has its fair share of hardcore fans, but even they might be oblivious to the inside jokes, secret gags, and Easter eggs hiding in each episode.

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The show actually puts a lot of effort into the one-liners that most viewers don’t notice, particularly the things left in the background. In fact, one of the show’s biggest Easter eggs is hidden in plain sight — in every episode!

Watch the video below to learn more.

As for those whiteboard equations? They do more than provide fodder for physics nerds; they also give a slice of scientific authenticity to the show.

“The science part is extremely easy,” Jim Parsons, who plays Sheldon, told NPR back in 2013. “We employ David Saltzberg, who is a physicist who teaches at UCLA. He not only fact-checks, but he supplies a great deal of [the material]. We need Sheldon to talk about something or teaching Penny whatever and [Salzberg will] come up with something. He sends over this diagram on this white board and he’ll throw in little inside jokes that I don’t find funny because I don’t know what the heck he’s talking about.”

Want more The Big Bang Theory? Click through the gallery to learn more about what each cast member makes.