 Before shooting the scene where Pulver identifies himself and tells  the Captain that hes been on the ship for "14months, sir",  James Cagney (qv) realized that he would have to rehearse the  moment with Jack Lemmon (qv) again and again so he wouldnt burst  out laughing during the actual filming. Lemmon agreed, and when the  scene was filmed Cagney claimed he was just barely able to hang on  with a straight face, even after all the rehearsal time.