In article , Jaques d'Alltrades writes:
| The message
| from "Franz Heymann" contains these words:
|
| What's a frog in this context?
| The indentation moulded into one face of a brick is known as the frog. I
| have no idea why.
|
| Probably from a similar-shaped indentation under a horse's hoof.

Which is not what the OED says. I agree with you, and think that
the OED is wrong.


Regards,
Nick Maclaren.