I'm in a zoo
But not in a jungle
I rarely come in pairs
But I'm in every puzzle


Some think I'm in a xylophone
But, I most certainly am not
You don't see me with a loan
But very strangely in a zealot


I'm in the magical prison of Azkaban
Well, can't you see?
I'm in the buzz of a fan
But, my oh my what could I be?

When you don't have it you want it, but when you do have it you want to share it , but you have to keep it. What is it?

You've got two jars, one of them fits exactly 5 litres, the other one fits exactly 3 litres. How could you get exactly 4 litres with these two jars? It is allowed to spoil some water.