This is a cognitive task aiming to assess whether kids can trade a small reward now for a bigger one later (it tests inhibitory control and ability to project oneself in the future). This experiment was conducted by comparative psychologists and, if I recall well, they also compared the kid’s performance to that of some primates to understand the evolution of the human mind.

Depends on the purpose. For documents (especially those on which people work collaboratively over long periods of time) I find YYYY-MM-DD ideal. It spares the issues around day or month first when Europeans and people from the US work together, the document are easy to sort and, if it takes more than a year to complete the project (as is often the case in research) things don’t get messy.

The fourth kind is the reason I hardly ever pet any cat XD