To get this achievement/ trophy you need the DLC called "Lord Of The Hunt"
A couple missions into the game you will do a hunt with Torvin where he will introduce you to the Wretched Graug. Right after a mission called " No Rest For The Wretched" will show up on the map. You will need to kill 20 archers with the projectile vomit to summon the warchief and his captains. Once you see them, run up to them and eat one of them quickly.
This achievement/trophy can be combined with "Wretched Retch"