More on Parseltounge...

[Steve]

I'm not quoting the original author because my comment (I hope) is
going to be very brief. 

Other people have said what I'm about to say but I'm going to *try*
and say it in the most concise possible way.

When Harry hears this vocal sound, he heard language and understands.

When we hear Harry make this same vocal sound, we don't understand it
as anything but noise.

Harry hears language; to our ears, Harry makes noise.

And that is exactly how the movie portrayed it.

In the book, nobody hears anything, JKR explains it to us in narative.

bboy_mn