purr, per

Purr or purr is the sound a contented cat makes, a low vibrating rumble, also made by some other animals--

This cat has a very loud purr.
You want the engine to make a purr, not a roar.


Purr may also mean to make the sound of a contented cat--
I can hear the cat purr from across the room.
"I'll be sittin' next to her and she'll purr like a kitten..."

Per or per ( rhymes with purr ) most commonly means for each--
We can't afford to spend more than a dollar per item.
If you buy more than a hundred, they'll be twenty-five cents per pair.
Our employer will reimburse us at a rate of thirty cents per mile.

Per is also an archaic ( no longer in use ) word meaning "by way of"--
Have this sent per the parcel delivery service.

Now that you know that, you can say--
"He's been feeding the cat at a rate of three treats per purr."