This is just so delightfully quirky and apropos of nothing, I want to share it: why breathing through a tube can be dangerous, explained by my good old friend Jason Turner, diver, chemical engineer, general smartypants: CO2 buildup in the breathing tube. Shallow breaths won't flush the tube of CO2, and you wind up pushing spent breath a bit backwards and a bit forwards. Your lungs get that burning feeling, you get dizzy and headachy, then you pass out from the reduced oxygen if you keep it up too long. With normal snorkels, it’s really hard to get to ‘too long.’ With long snorkels, the breaths must get deeper to sweep the CO2 from the tube, and because you chest is deeper, your breaths get shallower. Whoops. The good news is that this kinda takes care of itself: most people get tired and fed up with the effort and get out of the pool before hypoxia has a chance to set in.