When Sheldon and James Earl Jones share a sundae, a portion of whipped cream disappears and the cherry moves without either of them eating anything.
From 00:46-01:23, Penny is seen pouring a cup of coffee into a tall slender cup, then drinking it while the guys are trying to gain access to the queue for buying tickets to Comic-Con, but between 02:03-03:39, the cup is now flat and big like you'd see on the Friends series.
When Sheldon sings the final notes of "The Lion Sleeps Tonight," his mouth is not quite in sync with the words. Also, he moves his mouth away from the microphone just before the fade-out, but his voice can still be heard at the same volume.
In the list for "Sheldon-Con Possible Guests" Sheldon made a spelling mistake by writing Ian McKellen's last name as "Mckellan".