what's a sentence for whistle?

Answer 1

He/She let out a low whistle.

I heard the train whistle as it came around the bend.

Answer 2

There's the song from the Disney movie, Snow White, "Whistle While you Work."

You'll get other ideas from the examples in this site.

http://dictionary.reference.com/browse/whistle

Answer 3

Before posting anything else, go and search up the terms you have, on a dictionary online. They have many examples of sentences; which after looking at, you should be able to come up with your own.