Lawn Aerator Sandals

I don't know if there is a recognised generic name for these things but the label on the packaging is "Lawn Aerator Sandals". I thought I'd better blip them before I start using them - while they are pristine. Anyway this is another view of yesterday's little mystery. The extra shows them more or less attached to my gardening shoes.

Thanks to everyone who made a guess yesterday. The best answer was from "Mr Isbi", who got it exactly right.