When Leonard, Priya, Bernadette and Howard are having dinner together, Leonard's glasses are changed from a thin model to a thicker one between shots.
In Sheldon's 3-person chess game, he created a new piece called "The Serpent" who is able to poison other pieces. Snakes are not poisonous. They're venomous. Poison can be consumed, inhaled or absorbed through the skin, but venom must be injected into the bloodstream directly. Sheldon would not only know this, he would make a point of correcting anyone who implied a snake was poisonous.
Priya says that she shared a room with her brother growing up but earlier shows have made references to how wealthy they were and how many servants they had. If they had lots of servants, they most likely would not be sharing a single bedroom growing up together.
Raj says that nothing rhymes with orange, when, in fact, there are 3 uncommon words that do rhyme with orange: "Sporange", which is a Botany term for a sac where spores are made; Gorrange, a rare English surname; & Blorenge, a mountain in Wales.