The surrogate mother story arc was written especially for Lisa Kudrow because she was really pregnant with her son Julian.
One of the questions the guys get right is about Monica's categories of towels. When the guys & the girls move, several boxes with Monica's name & the towel categories are visible in the background.
One of the rare episodes not to feature a single scene in Central Perk.
Chandler, Joey, Monica, and Rachel play a game of who knows who better, with Ross being the question man. It appears that Ross is the one who actually knows all of them the best, considering that he came up with all of the questions and answers. However, it does make sense that he would, considering that he is Monica's brother, he dated Rachel, and he's been Chandler's best friend since college.