Revealing mistake: At the beginning when cutting the tomatoes onto the buns, Bob is not even coming close to the tomato in his hand, yet slices are falling off onto the buns. (00:03:50)
Revealing mistake: In the intro of the series "Honey and the Beaze" which Walt participates in, you can see Walt standing by a wall that reflects him, but there is no sign of Bob that usually would stand beside him. (01:01:10)
Revealing mistake: In the beginning when squirting ketchup and mustard on the buns, the angles the bottles are held at and how the condiments come out of them show that he is not actually squirting anything. It's all done with computer graphics. (00:03:50)
Revealing mistake: Right after May finds out Bob and Walt are conjoined she peels out in her car. In a close up on the twins you can see on Walt's right shoulder the suit they glued to him to conjoin the two. (01:09:05)
Answer: It's the Billy Stewart version of "Summertime" from George Gershwin's opera "Porgy and Bess".
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