How does a Ziplock bag water and a penny keep flies away?

A Ziplock bag filled with water and a penny is believed to deter flies due to the reflection and refraction of light. The water creates a shimmering effect that confuses flies, as they see distorted images and bright flashes, making them hesitant to approach. Additionally, the penny adds an extra reflective surface, enhancing the effect. While there's limited scientific evidence, many people swear by this simple and inexpensive method for keeping flies at bay.