Brothers Mortimer and Randolph Duke explain to William that they're commodities brokers. They explain what commodities are and provide examples of them. They then mention how they earn money: through the commissions of their clients.

Leonard is selling his share of the time machine and everyone is giving him offers below what he paid due to depreciation. He is also selling the rest of his collectibles and his friends argue and bid over the price.

Sheldon and Leonard are playing 3D chess which is a sequential game.

Raj and Sheldon partake in a series of juvenile tit-for-tat exchanges.

Leonard bids on a movie prop and ends up winning. He pays the amount he bid so this is a first-price auction.