Most bricks I have seen here in the USA have holes or no holes and have parallel sides, except for pavers which have an up-side and a down-side. I did see some old bricks removed from a building built in the 1800s that had a cylindrical recess about 1/2-in deep on one side, with a corresponding "bump" on the other side. these had been laid in the typical "running bond."
I am wondering whether the term "frog" relates to the the frog part of a horse's hoof that farriers worry about. This similarity would be negated with the bricks frog-up and enhanced with them frog-down.
--ShopShoe
