As much as i think about it I can't think of why blowing air in and out of a balloon is any better than simply holding it in the lungs (after taking it down like weed) apart from by hyperventilation making you lightheaded or by moving it around your lungs (in which case would a hold while taking smaller breaths in at intervals be a good idea, for nos or salvia)? Sounds to me like not exhaling it and inhaling it again would allow it to spend more time in your lungs so it could be absorbed quicker, please tell me if this is right.
