In waterboarding, water does not enter the air passages of the subject.

Quote Originally Posted by TwistedTails View Post
Would they drown without the slant? Probably not. Actually the slant is what does the work, water seeks the lowest level. By angling the subject (or just the subjects head ) water runs into the nose and fills up the back of the throat. Weather it is torturous or murderous is determined by a variety of factors but primarily how much air you are allowed between pouring.