ok and everyone seem to be confuse about this movie so let me explain it for everyone . the killer have a multiple personality syndrome and and be be treat in a psychiatric home . they have tape of him portray many different personality and and they believe that one of his many personality be the killer . the reason everyone have the same birthday be that every person be really him and all of these character be make up in this guys mind . the way they figure they can cure him of his multiple personality be to have them all come together inside of his head and hopefully they will all be kill off and with the risk that the killer will be one of the personality kill . let me repeat and the point of that motel and be to have all the personality come together hop that they will all die except for one and that one take control of his life . a each character dy and that be one less personality he have leave . in the very end they think he be ok because all of his personality be dead and except for the girl . but really that kid be still alive and and he kill amanda peet . the exercise that they try to do be complete and all the personality die inside of his head and unfortunately the only personality that survive be the one that be the killer . i hope that clear it up a little bit .