Ultrasonic Cat greenie laser???

Ok- This is really out there, but here goes.
I have a <5mw greenie from an ebay seller. It is not the best but for 10 dollars I couldn't resist. So I'm messing around with it - checking IR spillage with a digital camcorder and the sorts when I notice that my cats perk up when I push the button. Now the strange part is that I blocked the beam with my finger and pushed the button and the all perked up. Like they heard some sort of high frequency noise eminating from the laser. Any ideas about this??

B

perhaps cats just have a sixth sense for laser pointers!

My cats will run in from wherever they are if I even pick up the cat-toy pointer. I think they hear the particular keychain rattle noise. But I've also seen them perk up when I push the button even when it's not pointed where they can see it. I don't know if it's that particular click that makes them expect the red dot bug thingie is about to appear, or what. A $2 red pointer doesn't have a boost circuit, just a regulator, so there shouldn't be any high frequency sound.