Maybe b/c w/ a grav, you're pushing the smoke so deeply into your lungs (via gravity) that more of it gets absorbed, as opposed to just your inhaling power with the bong, it probably doesn't reach as far into your lungs.

no?
vej33 Reviewed by vej33 on . question about gravity bongs ok, i was just smoking my grav bong, and then switched to my normal bong. i noticed the smoke i was exhaling was MUCH thicker out of my bong. i dont get it, i hold my hits for about 5 seconds on both, but sometimes with the grav bong, almost no smoke at all comes out. i dont get it, i get it reeeeealy milky too. Rating: 5