After Howard dumps his belt buckles out on the bed, the position of several of them changes throughout the rest of the scene.
In season five Ep21, "The Hawking Excitation", Howard continuously denies Sheldon the chance to meet Prof. Hawking using multiple languages. However, in the Japanese language, vowels and consonants are extended which separates similar-looking words with different meanings. When Howard says "iie", he pronounces the much quicker "ie" which actually means "house".
When Sheldon visits Wolowitz at the engineering lab, the sign on the door says "resticted", not "restricted".
Raj claims that Sheldon "begged TNT to cancel Babylon 5 (1993)", but according to The Staircase Implementation (2010), Leonard, Howard, and Raj did not meet Sheldon until 4 years after the show had already ended production.
Sheldon wouldn't be able to fit in Bernadette's French Maid outfit, it would be way too small on him.
After revealing numerous belt buckles to Sheldon (for him to polish), Howard points out the irony of him only possessing one belt. Careful observation will show Howard wear various belts throughout the series.
Leonard says that Rasj is the 'group historian'. Sheldon has an eidetic memory, and throughout the series repeatedly acts as group historian.
Maintaining Hawking's wheelchair would be a job for a mechanic, not an engineer.