Hedgehogs!
I was doing some kettlebell exercises in the park opposite where I live - 100 swings, 100 high pulls, 100 windmills, 100 clean and press - and it was getting pretty dark, too dark to safely finish with 100 snatchs, another time.
Bearing in mind I was interrupted at the start of my 100 high pulls by a man and his dog, he seemed a bit keen, and well I thought talked a bit too long for an innocent chat with a stranger, so when I heard rustling in the trees behind me I thought 'boshi ken' check, 'mae geri' check.
I turned around and saw nothing. Then I looked a bit harder and saw a blob moving around on the ground. Cue: move in for a closer look. They can't half run for the size of them, unfortunately for some not as fast as cars.