If you’ve ever seen your cat staring at paper or pawing at the curtains, or your dog gazing off into empty space, a new discovery explains that your pets do indeed see something you cannot.

A paper published in the biological research journal Proceedings of the Royal Society B reveals that dogs, cats and many other mammals can see ultraviolet light (UV), providing evidence that cats and dogs do in fact see things that are invisible to the human eye. While some readers have speculated these animals are seeing spirits and ghosts, science reveals that this ability is not supernatural in origin, but instead rooted in biology.

Biology professor Ronald Douglas of City University London and professor of neuroscience Glen Jeffery of University College London co-authored the paper, which details their study of mammalian eyes. In their findings they detected UV sensitivity in the eyes of numerous mammals, including cats, dogs, deer, rabbits and rodents.

In fact, many animals of all types, from insects to birds, fish to reptiles, have UV vision.

Here are some things to know about UV light:

• Most of natural UV light comes from the sun
• UV light is invisible to the human eye
• Many substances can absorb and then slowly emit UV light
• It is what make black-light posters and fluorescent pigmentations glow
• Melanin, a pigment in our skin, absorbs UV light and darkens due to gained energy
• Suntans are the visual result of darkened melanin, as they gradually dissipate the radiation
• The skin can only absorb so much radiation before there is tissue damage, hence sunburns and 90% of skin cancers

Like radio waves, infrared, visible light and x-rays, UV light is radiation that exists on the electromagnetic spectrum, but has a shorter wavelength than visible colors. This shorter wavelength prevents the range of UV light from passing through the thickness of the lens in the human eye.

The study found that the thinner lens in the eyes of cats and dogs allow ultraviolet light to pass through, which in turn enables them to detect a world of information indiscernible to humans.

The Invisible World of Cats and Dogs

Because of their UV sensitivity, says Douglas, these animals have superior night vision to humans, and can see anything that reflects UV light. This includes:

• Patterns on flowers indicating to bees where to find nectar
• Polar bears and white rabbits standing out in a blizzard (snow reflects UV light)
• Butterflies using UV light as a communication system to find mates.
• Many flying insects look to the UV emission of stars as navigation references
• Scorpions glowing a vibrant green-blue color under UV illumination
• Urine trails and other animal secretions emitting UV radiation

Yes, that’s right, predators can follow rodent urine like a breadcrumb trail leading to their supper, and dogs can actually see other dogs’ territorial claims. Thankfully, we do not.

And when your pet stares obsessively at your curtains or blank paper, it may be that they are fixated on UV emitting fluorescents that sometimes are added to paper, fabrics, laundry detergents, cosmetics, black-light posters, safety vests and many other materials.

Ultraviolet Detection

There are always trade-offs, and with great night vision comes blurry vision in bright daylight. And while your cat or dog still cannot see ghosts or spirits, perhaps in time we can train them to detect things we cannot see ourselves, such as fires’ heat emissions, corona discharges, bodily fluids, skin cancer and intentionally hidden signs and trails.

Imagine for a moment a pet that could alert you to the heat emanating from a yet unseen fire, or a medical dog that is trained to be an early detector of skin cancer brought on by too much exposure to ultraviolet radiation.

For more information, check out this video from Animalist