First of all, find the Ermine by watching a scrum of kids chasing something around.
Position yourself in a place where you can watch the action, but where you are in no way hidden from the Ermine.
Next, pay no attention to your camera settings, or if you do make sure it is set on a slow shutter speed. Spot, one shot focus setting is desirable as well, to make sure that your auto focus does not track said Ermine.
Marvel at just how quick Ermine are, especially when chased by a group of kids. Marvel also at the Ermine's penchant for never pausing for more than a fraction of a second.
Trash the unusable photos upon getting back to the computer, and never, ever share them like this.