The animation is just indicating it is scanning, this will most likely be related to what you are actually doing at the time.
The main problem being there could be activity on many things at the same time, programs running in the background, browsing the web, etc. The issue then would be trying to pinpoint exactly what it was at that time, before you even got to the tray icon to check.
The Statistics section may well be your best bet given it displays the last 5 items of scan activity.