Whistling with acorns is a trick that is easy to learn and teach, plus, it is very effective at getting attention and amazement from friends. Additionally, it can save your life if you are lost in the woods and need a way to signal rescuers/ scare off wildlife.
Find an acorn cap. This is the brown part on top of the acorn. Make sure it is not cracked or deformed. Also the larger the acorn cap the lower the pitch.
Grab the acorn cap in both of your hands between your thumb and index finger with the inside of the cap facing you.
Put your thumbs up to near the top of the acorn. The sides of the knuckles of your thumbs should be touching each other.