When Penny is making French Toast, the amount of egg/milk/etc varies on the bread while she's holding it.
Sheldon (Jim Parsons) states "Bazinga! None of you ever see my practical jokes coming, do you?" This was reference to his previous comment about wanting to go to a Goth bar. Technically, this wasn't a practical joke. A practical joke "...makes someone seem silly and involves a physical action rather than words."
Sheldon says that he is using operant conditioning with Penny based on the works of Thorndike and Skinner. While he correctly states that the chocolates are being used as positive reinforcement (giving someone something to increase the likelihood of the behavior) He inaccurately describes mild electric shocks as negative reinforcement (taking away something to increase the likelihood of behavior), when according to Thorndike and Skinners work mild electric shocks would be positive punishment (giving something that would decrease the likelihood of the behavior). Ironically, Sheldon points out that people commonly make this error in "The Big Bang Theory" (2007) {The Focus Attenuation (#8.5)}.
When Howard is revealing to the group that his tattoos are only dyed sleeves, he points to the benefit of still being allowed burial in a Jewish cemetery. This erroneously implies that he would not be allowed if he had real tattoos. Although considered a sin, tattoos do not prohibit burial in a Jewish cemetery, according to Jewish law (Halacha). This is actually a very common misconception.
Sheldon refuses Penny's request to dance with her saying that in all of the infinite number of universes, he does not dance. However, in "The Agreement Dissection" #4.21, he states that he learned to ballroom dance growing up in Texas and later, he and Amy are ballroom dancing.
When Howard and Raj leave Sheldon and Leonard's apartment, Howard heads in the direction of Penny's apartment instead of towards the stairs.