Even though it's stated in this episode that Phoebe just discovered how loud Monica is while being massaged, in The One Where Rosita Dies (2001) Phoebe said that she had "only two clients all year and were the worst tippers in the world" she was referring to Ross and Monica, which means she had already given Monica a massage.
At 13:27 in this episode, you can clearly see Chandler is missing a part of his finger. According to other sources, Matthew Perry lost the fingertip of his middle finger on his right hand due to a childhood accident where he caught his finger in a door.
In the first season, episode 12, the closet door is slightly ajar revealing a neat closet.
The magna-doodle on Joey and Rachel's door has a picture of a hockey goalie.