Marcel the Monkey joins the cast in this episode. Left home alone on New Year's Eve, Ross (David Schwimmer) -- the only one of the friends who didn't break their "no date" pact -- "adopts" Marcel. Everyone loves the little simian except Monica (Courteney Cox), who has issues with Marcel's sanitary habits (or lack thereof). Elsewhere, Phoebe (Lisa Kudrow) may prompt a reclusive physicist (Hank Azaria) to give up the professional chance of a lifetime. ~ Hal Erickson, Rovi