#30DaysOfComics 4. Scrapey Scrapey Scrapey
Basically this SMBC comic.
Also, I tried to find a good visual reference for this, assuming it was a pretty standard cartoon Thing. Surprisingly little Google luck. I did find this video which is great but also a bit of a trial for the attention span challenged among us: http://www.youtube.com/watch?v=zoY_syxM6zM