The easiest way to do this on on the Acropolis level. Unless you are just getting to that part, you will need to redo it in Score Attack Mode. So, go to Expeditions, then score attack mode, select the Acropolis level, choose Tomb Raider difficulty and begin your game. Continue to the cutscene and until the enemies pop up. Run back to the tent and then use the poison arrows on the blob of enemies. Here is a video to aid you: