How do you make your guinea pig whistel?

Whatever you do, don't do anything mean to make it whistle.

What I find is that my piggies whistle when they are ready to eat and hear a food bag. Guinea pigs aren't THAT smart but they're smart enough to recognize the sound of the refrigerator opening or a food bag. So, if you feed them at a similar time, they'll learn the sound and whistle.

Then, you can just crumple a bag and you can hear them whistle. But give them a treat if you do this or they will not do it for long!