The washer itself creates only a small vibration. Inside an envelope, however, that movement causes the paper to vibrate as well. The broad paper surface moves more air than the small washer, amplifying the sound.
This is similar to the way the body of an acoustic instrument helps make the vibration of a string audible. The envelope is not merely packaging—it is part of the noisemaking mechanism.
Different paper materials can produce different sounds. A thin envelope may create a sharp buzz, while a greeting card or folded sheet of heavier paper may produce a lower rattle.
Is the Prank Safe?
The device is usually intended as a harmless novelty, but no startling prank is appropriate for every person or situation. A sudden noise may cause someone to drop an object, fall, panic, or react unpredictably.
Do not use this prank on:
- Babies or young children
- Older adults who may be vulnerable to falls
- Anyone with a heart condition
- Someone with severe anxiety or a strong fear of snakes
- A person wearing hearing aids or sensitive to sudden sounds
- Anyone driving, using machinery, carrying hot liquids, or standing near stairs
- Animals, which may become frightened or defensive
Never place the device in an envelope designed to resemble a bill, court notice, medical result, government letter, or other important correspondence. The joke should not create genuine fear or emotional distress.
It should also never be mailed without checking postal rules. An unexplained object inside an envelope may damage sorting equipment, tear the packaging, or appear suspicious to the recipient or postal workers.
