The "Slowly I turned" routine was apparently performed in two comedy films that were released in 1944: Abbott and Costello's Lost in a Harem and The Three Stooges short Gents Without Cents:
"Slowly I Turned" is the most common name associated with a popular vaudeville sketch that has also been performed in cinema and on television. Comedians Harry Steppe, Joey Faye (1909-1997), and Samuel Goldman each laid claim to this timeless classic of show business, also commonly referred to as, variously, "The Stranger with a Kind Face" (by clowns and clowning aficionados), "Niagara Falls" (by fans of The Three Stooges), "Pokomoko" or "Bagel Street" (by Abbott and Costello lovers), and "Martha" (by fans of I Love Lucy).
From Wikipedia's Slowly I Turned page:
RoutineThe routine features a man recounting the day he took his revenge on his enemy - and becoming so engrossed in his own tale that he attacks the innocent listener he is speaking to. The attacker comes to his senses, only to go berserk again when the listener says something that triggers the old memory again.
Typically, the routine has two characters meeting for the first time, with one of them becoming highly agitated over the utterance of particular words. Names and cities (such as Niagara Falls) have been used as the trigger, which then sends the unbalanced person into a state of mania; the implication is that the words have an unpleasant association in the character's past. While the other character merely acts bewildered, the crazed character relives the incident, uttering the words, "Slowly I turned...step by step...inch by inch...," as he approaches the stunned onlooker. Reacting as if this stranger is the object of his rage, the angry character begins hitting or strangling him, until the screams of the victim shake him out of his delusion. The character then apologizes, admitting his irrational reaction to the mention of those certain words. This follows with the victim innocently repeating the words, sparking the insane reaction all over again. This pattern is repeated in various forms, sometimes with the entrance of a third actor, uninformed as to the situation. This third person predictably ends up mentioning the words and setting off the manic character, but with the twist that the second character, not this new third person, is still the recipient of the violence. (However, in some variations - as in the Three Stooges short Gents Without Cents - the newcomer may be the attacked party.)
Abbott and Costello did a version for their television show which ended with Costello’s troublesome lawyer entering the scene. Costello asks for the lawyer to take the case of the storytelling stranger, and the lawyer says, "Help him out? I don’t know anything about him! What’s his name? Where is he from?" Costello whispers in the lawyer’s ear, to which the lawyer says aloud, "Niagara Falls?" Then he, of course, is immediately attacked. Steve Martin's character of Rigby Reardon had the similar trigger, "cleaning woman", in his film noir homage Dead Men Don't Wear Plaid.