John Ashcroft recently visited Knox College, giving a speech on “Leadership in Troubled Times”. One of the students asked him about a waterboarding case from WWII, where a U.S. war tribunal condemned a Japanese soldier for employing this technique on U.S. soldiers.

John Ashcroft Yelled at Me Tonight. No Joke – Daily Kos:
…It will be, sir, just give me a moment. The judgement describes this water treatment, and I quote, “the victim was bound or otherwise secured in a prone position; and water was forced through his mouth and nostrils into his lungs and stomach.” One man, Yukio Asano, was sentenced to fifteen years hard labour by the allies for waterboarding American troops to obtain information. Since Yukio Asano was trying to get information to help defend his country–exactly what you, Mr. Ashcroft, say is acceptable for Americans to do–do you believe that his sentence was unjust? boisterous applause and shouts of “Good question”
ASHCROFT: (angrily) Now, listen here. You’re comparing apples and oranges, apples and oranges. We don’t do anything like what you described.
ME: I’m sorry, I was under the impression that we still use the method of putting a cloth over someone’s face and pouring water down their throat…
ASHCROFT: (interrupting, red-faced, shouting) Pouring, Pouring, Did you hear what she said? “Putting a cloth over someone’s face and pouring water on them.” That’s not what you said before. Read that again, what you said before
ME: Sir, other reports of the time say…
ASHCROFT: (shouting) Read what you said before (cries of “Answer her #ucking question” from the audience) Read it
ME: (firmly) Mr. Ashcroft, please answer the question.
ASHCROFT: (shouting) Read it back
ME: “The victim was bound or otherwise secured in a prone position; and water was forced through his mouth and nostrils into his lungs and stomach.”
ASHCROFT: (shouting) You hear that? You hear it? “Forced” If you cant tell the difference between forcing and pouring…does this college have an anatomy class? If you cant tell the difference between forcing and pouring…
ME: (firmly and loudly) Mr. Ashcroft, do you believe that Yukio Asano’s sentence was unjust? Answer the question. (pause)
ASHCROFT: (more restrained) Its not a fair question; there’s no comparison. Next question

Well, how can a bound person prevent water from entering their throat if someone is pouring it over their face?

You can only hold your breath for so long.