this be a movie that will leave you think and be he or isn not he . while many people have complain about the ambiguous end and it give room for the audience to think and interpret it from the sign . this be my interpretation and theory and and i believe it be very sound . first and here be the plot . one day and prot ( kevin spacey ) suddenly appear in the midst of a busy train station . after attempt to help a woman from mugger and he be arrest and send to bellevue and and later transfer to dr. mark powell ( jeff bridge ) hospital . prot freely talk about how he come from the planet k pax and be here to do a report on earth . naturally and he be classify a a looney and be lock up in a low security level ward . he befriend the other patient and quickly convinces them of his story . in fact and he tell them he can take one person back with him . soon dr. powell be begin to question prot insanity and a the plot progress and it be hard and hard to prove prot wrong . in the end and dr. powell learn that prot be robert porter and a smart man who work in a slaughter house in new mexico and when his wife and daughter be murder . prot claim that he plan to leave for k pax at a precise time on the fifth anniversary of the murder . the time come and go and and powell find prot or robert in a catatonic state . one of the patient be miss and be never find again . on to my theory represent prot be not crazy . prot be from the planet k pax . robert porter be a friend of prot . on one of prot previous visit to earth and robert be a child and learn about the constellation from his father . prot and robert become best friend . after the death of his family and and robert slay the murderer and robert decides to commit suicide . prot be on k pax at the time and but he rush back ( in multiple of light speed ) to stop robert . so prot take over the thinking of robert and take over his body so to speak . awhile later and prot ( still inhabit robert body ) come to new york and be lock up . when he leave for k pax on july 27 and he take bess with him and but he must leave robert body behind . hence and we now have the catatonic robert . explanation or clue representprots knowledge of the planet around libra represent a prot say and any child know about their own system . only a few people on earth have an inkling about the system and and prot add to their knowledge . robert porter and while smart and know his constellation and be no astro physicist . dr powell feel choose by prot represent it true . prot could have leave the institute at any time and but choose not too . prot last word to dr. powell be and now that you have find robert . take care of him . prot be probably stay there to ensure a place for robert when he leave . super human ability represent it be a proven fact that prot have a significantly high sensitivity to sunlight and could even see uv ray . prot provide his usual k pax reason and but there be no earthly reason give . it be also mention that prot be give extremely high dos of medicine with no effect . help the patient represent throughout the movie and you see prot help the other patient ( or the patient discuss prot suggestion ) to a good sane world . while the psychologist balk at prot help and dr. powell talk at the end of the movie about the new live the patient be lead . the sprinkler scene represent the sprinkler be associate with porter home in new mexico ( which be ironically where roswell be ) . do porter associate the sprinkler with the death of his family . be her try to protect powell daughter from that horrible fate . i have a different point of view . it be assume that porter have commit suicide in a river . indeed and prot ( under hypnosis ) be greatly concern about robert . i believe that prot associate the danger with the water and not the sprinkler . he be try to protect the girl from watery death and like he do robert . hypnosis represent dr. powell feel that under hypnosis he can uncover prot true identity and but while prot give plenty of information and he never give up his prot persona and claim homeland of k pax . the security camera represent why would the camera just give out for no apparent reason . mysterious disappearance represent first and prot disappear for a few day to his trip up north . funny and the patient be not at all alarmed . indeed and they try to reassure the doctor . sometimes i think they understand good than the staff . naturally and the most telling disappearance be of bess and the winner of the essay contest . not only do she disappear at the approximate same time and but the only remain clue be her win essay . this be only my humble theory . you can conclude what you want . you can take dr. powell theory and that prot be merely a persona take up by robert porter to mentally defend himself from reality and but that would be give up too many plot hole .