6x17 "The One with Unagi" "The One with the Mix Tape"

Rachel and Phoebe take self-defense classes. Ross, who had previously practiced karate, tries to attack them by surprise and convince them that they lack unagi, supposedly a state of "total awareness". In reality, as pointed out by Phoebe and Rachel, unagi is just a Japanese dish (in karate, zanshin is the state of total awareness). Chandler and Monica celebrate Valentine's Day several days after the actual date because of their schedules, but they forget to make each other homemade gifts: Monica gives Chandler one of Phoebe's "sock bunnies", and Chandler gives Monica a mixtape, which was originally a present from Janice. Joey decides to get money through medical research, but learns that the only study available is for identical twins, which pays $2,000. As a result, Joey tries to find someone to play his twin.