Like other behaviors—the blep, for example—the feline urge to perk up upon hearing Pspsps doesn’t have a proven scientific explanation; and researchers aren’t exactly pouring time and money into trying to solve the mystery. But cat experts have some pretty compelling theories.
An especially popular one has to do with frequency. Cats can hear sounds at higher frequencies than humans, and the s sound operates at a higher frequency than most other human sounds. When each s sound is interrupted by a p, veterinary behaviorist Katherine Pankratz told Inverse, it “creates a staccato sound that is abrupt and attention-grabbing.” And because Pspsps stands out from whatever else humans are usually saying, cats may be more inclined to investigate where it’s coming from.
The tendency to react to Pspsps could be less about what it doesn’t sound like—other human chatter—and more about what it does sound like: prey. Péter Pongrácz, a professor of ethology at Hungary’s Eötvös Loránd University, told Reader’s Digest that rodents’ “high-pitched squeaking vocalizations are roughly approximated” by s and other hiss-like sounds that humans can make. Pet Keen points out that Pspsps may also call to mind other noises that cats pay attention to, from rustling leaves and buzzing insects to the cautionary hiss of a mother cat who senses danger.
It’s also possible that cats generally respond to Pspsps because we’ve inadvertently trained them to do so. If you’ve been Pspsps-ing your cat for a while, it may now correlate the call with cuddles, treats, or just attention in general.
As for where the term came from in the first place, Reader’s Digest suggests that it’s a truncation of “Here, pussy, pussy, pussy”—popularized in part by “Pussy, Pussy, Pussy,” a 1930s song by the Light Crust Doughboys. In fact, the tempo is fast enough that it almost sounds like they’re singing “Pspsps.” Feel free to play the track for your cat to see if it agrees.