Mr. Yuk is a neon green circular sticker with a cartoon face on it. His face is scrunched up with his eyes squeezed tight and his tongue is sticking out of its mouth. It's the face you make when you taste something disgusting. He's the pictorial embodiment of the sentiment of yuck. Aptly enough: he was designed to be the symbol for hazardous substances, aimed at deterring children from ingesting them. The idea what that if you saw a Mr. Yuk sticker on something around the house, it meant that that something was poison.Friend of the show, Gillian Jacobs, is a BIG FAN of Mr Yuk, who turns out to be a hometown hero of her beloved Pittsburgh, and talked Roman through the origins of the mean, green face that was meant to save children from their worst impulses.Plus, we revisit another story about warning symbols from our archive: the quest to find a symbol that would warn future humans of dangerous radiation 10,000 years in the future.Mr Yuk