The jug and the bird
In my 5'th grade, the new professor of Mathematics told us a puzzle: there is a jug with water staying in the desert, and a bird wants to drink some water. However, the jug have a tight neck, like the old Greek pottery for olive oil: it is like a sphere at the bottom, becoming tight while going up, only to enlarge a bit at the entry. At least this is how I imagine it. What is clear, the bird cannot reach the water because the head/beak are too big for the jug entry. How can the bird drink some water from the jug?