What's that indentation called?

 This Indentation, you've probably seen it before.

This Indentation, you've probably seen it before.

This feature of many bricks is commonly referred to as a 'Frog' - there are many arguments around the internet with wildly varied explanations however, below is one that seems to make the most sense.

The actual term “frog” comes from the dutch word “kikker” Traditional brick making consisted of a wooden box which a “kicker” in the middle was used to force the clay out wards to form the arrises.
— https://www.theguardian.com/notesandqueries/query/0,5753,-67944,00.html

What are your thoughts on the origins of this unusual name? Should the 'Frog' being placed facing up or down whilst laying bricks? Why don't modern bricks have 'Frogs?

frog brick.png