THC is a bronchial dilator, which means it opens up your lungs, that's why you get that unsuppressable cough. it's better just to let yourself cough, cos you actually cough out a lot of the bad shit that's in your lungs (carcinogens etc).
I've never actually been able to figure out the red-eye thing. if i cough really hard for any reason (stoned or not) my eyes usually water or go red, but as for when i smoke up, it seems like sometimes my eyes are white as normal when i'm fucked, sometimes i look fucked when i'm not that baked at all, but most of the time when i'm baked my eyes are just a bit glazed and yellowy... but yeah it does seem like different bud has different red-eye impact. wierd.

peace