Chainstay question

This might sound weird, but I never noticed this until last night, when I had the bike upside down on the kitchen table to clean it (where do you guys clean YOUR bikes? )

Anyway, I noticed, for the first time, what first looked like a crack on the bottom of the right chainstay.  I freaked out for a moment, but the more I looked at it, the more I realized it looked machined, rather some kind of stress-related cause.

It almost looks like the canopy on a jet fighter.  It's only perceptible when you're right up close, but the fact that the lines were so smooth, and that they formed an apparantly symetrical section, made me think it was there by design.

Hopefully just a dumb question . . .

Nothing to worry about, right?