That sad puppy look your dog gives you… that look that Cali uses every time we’re within a block of her favorite ice cream stand … that look has been perfected by dogs over millennia. It’s no wonder we’re helpless to resist it!

It turns out that dogs’ “expressive eyebrows” enable them to raise their inner eyebrows in a way that makes their eyes look larger and, to humans, sadder. A study found “compelling” evidence “that dogs developed a muscle to raise the inner eyebrow after they were domesticated from wolves.”

What’s more, it’s mostly our own fault for breeding these manipulators: A Science Daily report on the study suggests that this eyebrow muscle, which wolves lack, “may be a result of humans unconscious preferences that influenced selection during domestication.”

It’s working out well for the dogs. The expression elicits a strong response from most humans who feel protective toward the “sad” or “worried” dogs. Dogs who use this eye movement get adopted faster from shelters, according to the study.

The muscle difference evolved very quickly, according to researchers, and seems to have had an outsize impact on human-dog relationships. Eye contact plays a huge role in dog-human communication, and the dogs have clearly learned to use their anatomical gift to full advantage.

Humans pay close attention to eyebrow movement, even if we aren’t really aware of it. “In humans, eyebrow movements seem to be particularly relevant to boost the perceived prominence of words and act as focus markers in speech,” the study points out. It hypothesizes that we’re especially tuned in to eyebrow movement because it “is a uniquely human feature.”

Or was. Until the dogs figured out how to hijack it.