When the arrow is moved to a particular distance behind the glass, it looks like it reversed itself. When light passes from one material to another, it can bend or refract. In the experiment that you just completed, light traveled from the air, through the glass, through the water, through the back of the glass, and then back through the air, before hitting the arrow. Anytime that light passes from one medium, or material, into another, it refracts.
Time Lapse Map of Covid-19’s Spread Across the US
N. Bauer used J. Hopkins University data for individual counties since the beginning of the pandemic to visualize the spread of the virus.