A single one-off accidental click? Don't worry about it, it is of no consequence.

ok thanks, it is even image ad so i think he won't lose much/any

An image? You're doomed! Doomed, I say!

/not really

Yeah wouldn't worry, accidents happen and the guys and gals at Google are aware of that. It used to be possible to contact them about this and in my more paranoid past, I actually did. I'd say it happens to me about once or twice a year. Cat jumping on my laptop and somehow managing to hit an ad was the most recent (Seriously.. it really happened!)

It happens. Google knows that.

i clicked an ad accidentally once and sent off an email to google explaining it, and all that happened was i got a canned response back with a line that said don't bother sending any more emails because their program discounts these kinds of clicks anyway.

I've had the exact same experience as Londrum. I can honestly say that in the last four years or so I've clicked on probably only one of my own ads.

If I ever do again though, I'll probably send Adsense email stating so. But not because I think I need to but because historically Adsense was such as jacka** about this type of thing. If I can waste even a second of their resources throwing something that never should have been an issue back in their face, I'm happy to do so.

Imagine, establishing a click-through program where the publisher didn't even have the option of declaring clicks from your own IP (or whatever method they have finally found to use) as needing to be disregarded, yet these very clicks could get you booted from their program. How utterly lame.

Cat jumping on my laptop and somehow managing to hit an ad

But if the cat ends up buying cat food and convert well for advertisers, it may not be discounted and you won't be smart priced.

It would depend largely on what the cat did after it landed on the site.

Number of page views, time spent on site, etc...

Of course if the cat actually purchased something you might even get any smart pricing you've incurred reversed.

Your milage will vary depending on the cat, of course...

Spoke to cat.. Cat blamed it on the mouse. Mouse thought AdSense ads were looking a bit cheesy these days, hence dropping CTR.

ROFL ^^^^^