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As Sheldon's work is still relatively new in dark matter and as Raj hears about some ground breaking work in mines that may have major implications in both theoretical physics in dark matter as well as astrophysics, Raj suggests that he and Sheldon may want to get involved in this work, which would mean spending time in underground mines at twelve hours at a time. The environment would play upon most of Sheldon's darkest fears. But Raj is able to convince him that they should simulate what working in such as environment together would be like before they make a definitive decision. Being alone together may give Sheldon and Raj time to think about more than just being in a dark, hot, humid and enclosed environment with no toilet. Meanwhile, Penny has sold the car that Leonard bought her since the pharmaceutical company has given her a car for work. She wants to give the money from the car sale back to Leonard. This gesture brings up issues primarily around Penny's new financial self-security, and what that means for their history of Penny largely being reliant on him in paying for things. As they argue about money in general, they feel that they should ask for advice from people who should have a better idea of what they are going through. The fact of asking leads to Leonard and Penny coming to some conclusions about their own situation that they were not expecting.