I came across this in some bizarre round about way after watching a video on the effects of cocaine.
Flakka has the effect of giving you extreme paranoia and a physical appearance of a zombie, with all the mannerisms. Truly terrifying from what I've seen so far on YouTube and it's a sure- fire killer, often after the very first dose.
This video is decidedly tame in comparison to others which you'll see available if you're so inclined.