Guys, on GTA V game internet there is website which you can take a part of courier job. There is a test and later after test a mini game where you have to eat 10 balloons to unlock the missions.
I have tried really many times to put all 10 balloons inside that poor guy, and it always used to explode, but I found out, that you need to watch his heartbeat and when heart is small then press x to eat balloon. Later on it will be heart beating very fast so it's going to be difficult to pass it, but I did it So good luck with it.
I know many people who tried tons of ways but always fail on 9th ballon. Anyway the answer is HEART. watch it's beats
Is your lung capacity stat full, by any chance?