Cats manipulate humans by embedding an urgent cry sound into their purr.Cat owners who think their cats control them now have some scientific confirmation: Animal vocalization experts have just identified a special manipulative purr that felines have evolved, in part, to get what they want from people. The newly identified vocalization, called "solicitation purring," has never been acknowledged or studied before, although cat fanciers, such as the study's lead author Karen McComb, are quite familiar with it. "In the case of my cat, if he sees you stirring from sleep at all in the early morning he will immediately switch into giving this solicitation purring and position himself next to your head so you get the full impact," McComb, a reader in Behavioral Ecology at the University of Sussex, told Discovery News. She added, "Asking around, I find I'm not the only one who, if I wake up early, often lie pretending to still be asleep so my cat doesn't start this!" McComb, who has analyzed communication and cognition of elephants, lions and many other mammals, decided to investigate what could be behind her cat's early morning purring. She and colleagues Anna Taylor, Christian Wilson and Benjamin Charlton examined the acoustic structure of recorded cat purrs. The team determined purrs are not all the same, since one contains an embedded, high-pitched cry. This resulting combination makes up solicitation purring. McComb explained that what cats seem to be doing for the special purr "is producing the low fundamental frequency and its harmonics by muscular activation" -- what has been associated with typical purring -- "but also voicing a cry, probably with the inner edges of the vocal folds, which is then superimposed on the sound's frequency spectrum." The researchers recorded 10 cats purring. Some of the sounds contained the cry, while others didn't or were processed to have the cry component taken out. Fifty human participants then listened to the sounds, described in the latest issue of Current Biology. Virtually all listeners, whether or not they owned a cat themselves, identified the solicitation purring sounds as being more urgent than others. Sensitivity to this type of purring may even be innate in humans, drawing from a primal drive to respond to crying babies. "Cats have about the right size of vocal folds to produce a cry that is similar to a baby's, so there is a coincidental element," explained McComb. "In fact, the meow can sound remarkably like a crying child, which will be particularly effective with humans." Cats purr to each other, but the scientists found felines really exaggerate their solicitation purring when communicating with humans, making felines near impossible to ignore. Georgia Mason, a professor and Canada Research Chair in Animal Welfare at the University of Guelph, told Discovery News she was pleased to see that "this careful work shows there are at least two types of purring: the shrill ones cats wake you up with, and the relaxing one they do at other times." "It makes me wonder whether dogs and cats learn to make sounds we find particularly hard to ignore, or whether we have selected for animals whose signals we find naturally recognizable and comprehensible," Mason added. Both she and McComb hope future studies will continue to unravel the mysteries of cat vocalizations, since they believe purring alone may be much more complex than previously thought, with various types of purrs, such as those emitted when cats are in pain, conveying different information.