i thought ihad a way to explain it, but that doesn't work with grav/waterfall bongs because you can see the smoke before you inhale it, anyways my theory was that you weren't really making the weed smoke, or just lightly smoking, and the rest was just vaporization, leading to the feeling of a getting a huge hit, but when you exhale there's barely any smoke, if any at all.. but yea you can see all the smoke in grav/waterfalls.. so that can't be it.