How to cry in a scene

Sometimes you get all teary eyed in a scene because an incredibly gifted, Oscar-winning actor is giving an emotional, beautifully acted speech about his character's dead daughter 4 feet in front of you.  And then sometimes, 10 takes later, you have tears streaming down your face in the scene because as soon as he started talking you really had to cough, until by the end of the very long take, holding the cough in hurts so bad that tears are pouring.... Both work.