Which can mean only one thing: Autumn.
And that in turn means hedgehogs.
A I don't know where the little pincushions hide in the summer, but in spring and autumn they are everywhere. Probably looking for food.
And this means I have to notice of every bump on the path before my dog does, and get away from it, lest it be an hedgehog and I have to spend the next minutes prying his mouth open and getting a spiky ball of fleas out.
No, this dog isn't the most intelligent creature to ever live. He's been trying this for the last seven years. And the only one who's learned something seems to be me. (I'm getting really good at telling apart stones from hedgehogs at a distance in the light of my bike's lamp.)