The purring cat. It may well be considered the epitome of contentment. But there’s much more to purring than meets the ear.

Research is starting to shed some light on purring -- starting with how cats do it.

How do cats purr? Experts have offered a number of theories over the years. Most now say that purring begins in the brain.

A rhythmic, repetitive neural oscillator sends messages to the laryngeal muscles, causing them to twitch at the rate of 25 to 150 vibrations per second (Hz). This causes a sudden separation of the vocal cords, during both inhalation and exhalation - the unique feline vibrato.

“Opera singing for cats,” is what animal behaviorist Karen L. Overall, VMD, PhD calls it. But the purr is usually so low-pitched that we tend to feel it as much as hear it.