There's Something Horribly Wrong with This Picture...

Summary
After going over a few illustrations by Trevor Henderson (a Canadian horror artist known as the creator of Siren Head, Long Horse, Cartoon Cat and others alike), Mark and Ethan decide to make their own picture within the next 30 minutes by hiding distorted visual elements in normal looking images. After comparing their results, the two ask their audience to submit similar type of work to the Unus Annus subreddit for them to potentially make a video on it. Nearing the end of the segment, Ethan exclaims "Well, thank you for watching and don't forget, always look behind you", followed shortly by a brief flash of a disturbing, shadowy figure (featured on the "HONESTLY TERRIFYING" thumbnail) overlapping the screen, as the video comes to a close.