[Traubenfuchs]

Liquid breathing hurts?

[Tildey]

Your anti-drowning reflex kicks in, which is fairly unpleasant, and I don’t imagine the lungs are used to a fluid with that much viscosity or mass

[celticninja]

I'm guessing, with the reference to amyl nitrate, they are assuming that whatever is stuck up your ass to facilitate this breathing process, is going to hurt.

[kayodelycaon]

Having gas pumped into you intestines is quite unpleasant. (Woke up mid-colonoscopy, not fun.)

[jensenbox]

The article is not referring to using your lungs to breath...

I can only imagine they way they are indicating the administration of the oxygen would be painful.