Wallet card with a remnant of the horse-and-buggy era

In New York City or any other older town, you may notice that the gates near entrances often have an opening near the bottom, with a thin edge. Do you know why?

One of the advantages of living in the age of the automobile, is that cars don't leave manure in the road when they go. Walking through a ninteenth-century city meant stepping in horse leavings, mud, garbage, etc. Since a proper gentleman wouldn't want to track that stuff into the house, these bootscrapers were a handy way to discreetly clean one's boots before stepping inside.