Hi Melissa! I am just now finishing up a different book by Patrick DeWitt - French Exit. Interesting to hear that you found The Sisters Brothers to be mainly dark with some comic tones. French Exit is very different. It's clearly meant to be funny and all the characters are quite eccentric and get into bizarre situations. I think I will have to skip The Sisters Brothers because of the animal violence, though 🙁
I seem to be the odd one out on that. It might have been the gruesome animal scenes that gave it that extra darkness for me. I watched a trailer for the movie and they also seemed to rely heavy on the comedy element