The top snowflake is a mirror of sorts, reflecting the light from the flash back to the camera. In almost every other circumstance, you’d call this “glare” and avoid it at all costs. In the case of snowflakes, it makes them glow.
The snowflake in behind is on a slightly different angle, making the reflected light bounce back on an angle different from that of the camera (appearing clear). The back snowflake is unique in it’s own right, taking on a triangular shape while keeping six sides.
Every snowflake is not only unique, but also has its own curiosities to ponder.