I remember seeing the trick on Tomorrow's World (a UK science TV programme) back in the 90s. Can't find a link to the particular episode though.

I was doing this in the mid eighties... think a teacher showed me it but can't remember... didn't have tv.

I'm pretty sure I saw it featured in an article in Highlights for Children during the 80s.

https://en.wikipedia.org/wiki/Highlights_for_Children

I learned it in australia many years ago from these guys: https://www.youtube.com/watch?v=DYBw7k_8EbE

Do Australians commonly say "elephant" to count seconds as the presenters do? In the U.S. it's usually "one-thousand" or "Mississippi". (I guess I can imagine that Australians wouldn't say "Mississippi"!)

I've never heard of "elephant", no. (Sydney here)

or 'chimpanzee'!