Monica: (about the twins) We can't split them up.
Chandler: Why not? We could give each of them half a medallion, and then years later, they'll find each other and be reunited. I mean, that's a great day for everybody.
Chandler was referring to the movie The Parent Trap in which identical twins, both played by Hayley Mills, are separated at birth and reunited at summer camp. They discover the truth through a locket that was split in half and given to both girls.