You sometimes see pages blocked or hear the "bark" when no one is browsing on the computer.
K9 Web Protection examines all requests to the Internet that come from your computer. Some programs installed on your computer will make requests to the Internet in the background, even when no one is logged into the computer. These background programs might be very useful (like Microsoft Windows Update) or malicious (like spyware or viruses).
Additionally, some web pages will access several sources for the information on that page; this is why you may sometimes see several entries in the View Activity log all with the same time.