That thing which crawled

It took me a while to realize that the little grey thing moving on my notebook was not my imagination, but a scarily tiny creature. He looked so fragile. My first impulse was to blow him off the paper. But I stopped myself, for he was more interested in scrutinising what I was reading then. He walked a bit, then paused; walked,paused, and sometimes ran too. It looked as though he was searching for something in the vast forest of black lines on paper. A place to set up his home, maybe? He should have been disappointed.
He never quit, though. Just when he had finished travelling the entire length of the paper, he started again in the diagonally opposite direction. His tenacity fascinated me - what did he want?
Just then, I sneezed.
I opened my eyes. He was nowhere to be seen, the little crawly spider!