Open the console. This page makes a post request asking for JSON response when the response will not be valid JSON.

Ideally, when it fails to parse the response as JSON, jQuery should error, or log using console.warn() or console.error(), or invoke the callback function passing null, undefined, or some other sigil indicating failure.

Instead, jQuery 1.4.2 does nothing at all, and users are left to wonder why their callback isn't being invoked when they get a single character wrong in their JSON.