Here is a whimsical limerick by Ronald Knox:

There once was a man who said: “God

Must think it exceedingly odd

If he finds that this tree

Continues to be

When there’s no one about in the Quad”.

Dear Sir

Your astonishment’s odd

I am always about in the Quad;

And that’s why the tree

Will continue to be

Since observed by

Yours faithfully

God.