Even though many sources claim that Anthony Quinn won his Best Supporting Actor Oscar for appearing a short 8 minutes in the movie, his performance actually lasts 22 minutes and 40 seconds.
Commissioner De Smet:
You are now qualified for evangelical work, under the auspices of The Belgian Committee of the Messengers of the Faith. May the lord guide you, and sustain you in all your ways.
Dr. Peyron: Congratulations Dr. Gachet, a very creditable group of young men.
Commissioner De Smet: Now ...
Dr. Gachet: ...
At Arles, when Paul Gaugin is explaining his philosophy, Vincent mistakes him for Theo saying "but Theo, err Paul ..."
It seems to be an error on Kirk Douglas's part, but is, in fact, in the script. The whole point of the line is that van Gogh views his conversation with Gauguin as nothing more than an extension of talks he's had with Theo since childhood.