Click here to launch an XMLHttpRequest.

On subsequent requests the XMLHttpRequest is read from cache. To see this yourself follow these steps:

1. Clear your cache.
2. Fire up a packet sniffer, such as LiveHTTPHeaders.
3. Click on the XMLHttpRequest link. You'll see the request to beacon.gif in your packet sniffer.
4. Click on the XMLHttpRequest link again. You won't see the request to beacon.gif because it was read from cache.