Rails, partials and AJAX.. what am I missing?

It took me a little while to wrap my head around this too, but the RJS
is translated to Javascript automatically for you, returned to the
browser, and then executed in the browser - and all this happens
asynchronously with regards to user actions in the browser.

Now, what makes everything fire off to begin with, is just as you said
- a button, link, or internal timer (like with

Getting back to your original problem - what happens if you comment
out the shake effect, and only do the div replacement with your
partial. Does the cart update correctly?