I finally saw a yellow weasel!
It's completely invisible in this photo, having bounded out of frame into the bushes, but it was really cute - roughly the color of an orange cat, with a little pink nose and twitchy whiskers.
Yellow weasels are not that uncommon in Shanghai - you'll sometimes catch a glimpse of gold fur blazing past you at night - but I'd never actually seen one up close, or during the day. They eats rats, which are a plentiful food source here. Even more glamorous, the one I saw had been rooting around in the garbage.
It makes me really happy to see wildlife finding/making a niche in the crazy, dense, ultra-urban metropolis of Shanghai. Maybe next time I'll even get a picture.