Jill Clayburgh's proof of the "Snake Lemma" at the very beginning of the movie is technically perfect. In Charles A. Weibel's book, "An Introduction to Homological Algebra" (Cambridge U. Press, 1994), there appears the following: "We will not print the proof (of the Snake Lemma) in these notes, because it is best done visually. In fact, a clear proof is given by Jill Clayburgh at the beginning of the movie 'It's My Turn.'"