In Uncharted 2: Among Thieves and Uncharted 3: Drake's Deception, Drake will use the term "Kitty got wet". This is a phrase said in the co-op mode of Uncharted II, and within Chapter 9 of Uncharted 3. The phrase was improvised by Nolan North, and originates from a term used by his then-eight year old son while they were playing Wii Sports. After beating his father, Cooper North exclaimed that "Kitty got wet", referring to the fact that cats dislike getting wet, just as people don't like losing.
The "Strange Relic" treasure that can be found in all Uncharted games is actually a Precursor Orb from the Jak and Daxter series. When the symbols on it are translated it says "Naughty Dog, Madman".