For me it is the fact that our blood contains iron. I earlier used to believe the word stood for some ‘organic element’ since I couldn’t accept we had metal flowing through our supposed carbon-based bodies, till I realized that is where the taste and smell of blood comes from.
But basic math means that those are the exact same thing. Divisible by 4 means multiples of 4 means every 4 years, right? It seems more likely that they “happen when the year is divisible by 4” came about after they said “let’s do it every four years, but we have to phrase it more officially when we write it down.”
You haven’t read the other rules
Not really. 1896 was a leap year, but 1900 was not.
The leap year after 2096 will be 2104.
Edit: an interesting way to put this is, 2000 was the only year in 4 centuries where the year starting the century was a leap year. Next such occurrence will be in 2400