Visible crew/equipment: When Leonard, Sheldon and Penny are eating lunch for the first time, Penny sits on Sheldon's spot, Leonard then tells him to "Just sit somewhere else." He then walks over to his desk chair and contemplates sitting there and in the bottom left of the shot there is a chair with 4 false legs, and one large leg running down the middle. (00:08:20)
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: At the very start, Raj walks over to his seat and a tape marker is visible on the floor. (00:00:05)
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Leonard opens the door at the start a yellow tape marker is visible in the centre of the door way. (00:00:40)
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Sheldon is mentioning about the coffee table having a garage sale, there is a shot of Leonard with all the stagelights reflected in the kettle. (00:06:40)
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Penny is having a go at Sheldon and Leonard, there is a shot of some metal pans with stage lights visible in them. (00:12:30)
The Hamburger Postulate - S1-E5
Visible crew/equipment: At the start when we see the guys sat at the table, a small white tape marker is visible on the floor where Penny will stand in a few minutes. (00:02:30)
The Middle Earth Paradigm - S1-E6
Visible crew/equipment: When Sheldon is being asked not to embarrass Leonard, the stage lights can be seen in the pans behind him. (00:05:10)
The Jerusalem Duality - S1-E12
Visible crew/equipment: When Dr. Gablehouser is giving his speech about Dennis joining them, stage lights are reflected in his glasses and his wine glass. (00:16:30)
The Vartabedian Conundrum - S2-E10
Visible crew/equipment: When Sheldon and Leonard are making breakfast, stage lights are reflected off a milk bottle.
The Maternal Congruence - S3-E11
Visible crew/equipment: When the four (Leonard, Penny, Sheldon and Beverly) are driving to the airport at the end, the studio lights are reflected in Beverly's sunglasses.
Chosen answer: The song is called "Dark as a Dungeon" and was written and first performed by singer-songwriter Merle Travis in 1946. It has been performed by a wide array of artists, including Tennessee Ernie Ford, Harry Belafonte, Dolly Parton, Queens of the Stone Age, Kathy Mattea and Amy Grant. But it was made most famous when it was performed and recorded by Johnny Cash during his concert at Folsom Prison in 1968. According to Wikipedia: "It is a lament about the danger and drudgery of being a coal miner in an Appalachian shaft mine. It has become a rallying song among miners seeking improved working conditions."
Michael Albert