METAL GEAR SOLID 3: Snake Eater - Master Collection Version

The description is misleading, the achievement name is what you should follow. Getting the guard to eat a poisonous animal or mushroom will not count. Instead, you need to capture (not kill) any poisonous animal, equip it from your backpack, and then throw it at a guard. The animal must hit the guard for it to count. You should see a hilarious animation of the guard combating the hostile fauna.

The animals that will count include the cobalt blue tarantula, emperor scorpion, coral snake, king cobra, Thai cobra, and the Taiwanese cobra.

The animal must be alive when you throw it. I tried using a dead coral snake on a hungry guard and it killed him outright and I did not get the achievement.