It's a dog's light

Dog owners are often so busy during the day that they only have time to walk
their dogs at night. Hence the huge popularity in Japan of a dog leash that
glows in the dark. The Wanwan (“doggie”) Line is made of transparent
polyurethane with a flashing LED at one end that transmits light through the
leash. The flashing red leash is easy for pedestrians and cyclists to see in the
dark. Its manufacturer, Matsushita Battery Industrial, decided not to use a
light inside the leash itself in case the dog chews through it.