When you only link to the image you lose a very important part of xkcd's content (the alt text): http://xkcd.com/230/

And for those on an iPhone or Android phone: http://m.xkcd.com/230/

Would just like to note that [in the xkcd comic] he should have used her abdomen or back to take notes. The chest has an unfavourable topology for that kind of thing.

Yes I have empirically proven this.

[pedantic]

Topology? AFAIK, all of these are homeomorphic to a piece of paper.

Topography != Topology.

While I'm not sure if there's an actual fusion in the depths of the naval, for practical purposes, the abdomen can be considered homeomorphic to the punctured plane, and treated accordingly.

... "for practical purposes" ...

Sigh. I guess I'll have to turn in my pure math degree.

You've not considered any possible piercings ;)

Depends on the chest. Or abdomen for that matter.

There speaks a man of experience!

Well I like the kind of girl whose chest is impractical for writing :P

While I'm sure spherical writing is all the rage in some circles, I prefer nice non-infinite straight lines ...

... I wonder if an algorithm could be extracted for the best helix function to use as the line basis to write on chest in regards to economy of space and ergonomy of writing.