How to loudly whistle with one hand To whistle loudly with one hand start by rolling the tip of your tongue toward the back of your mouth. Keep the tongue rolled back and take the your index finger and thumb and put them together to form a circle. Put your fingers in your mouth touching the tongue. Close your mouth and lips down around the two fingers and blow out. The air moving through your fingers and teeth makes the whistle sound. The harder you blow out the louder the whistle will be. All it takes is practice to get this whistle down. With a little bit of practice you will be able to whistle really loud.