I have long been a fan of 19th Century art and was quite young when I started reading everything about it I could find. One painting that I always found quite anomalous was Francisco Goya's
Saturn Devouring His Son. I understand the mythology behind it and the technique, but something about the inherent darkness and ugliness in the painting just never resonated with me on a rational level.
When I read about Gosnell's butcher shop a few years ago, the painting was the first image the accounts evoked in my mind.