Hundreds of gigabytes of horse porn, right in a folder on his desktop called "horse". The thumbnail of the folder made it incredibly clear what the folder was and what was in it, which was made extra clear by the max zoom his desktop icons were set to. (it was like, no joke, almost 1/10th the screen).

Fun fact: that was the day I learned my state doesn't have mandatory reporting laws for animal abuse, only csam.