The riddle
What Is Full of Holes but Still Holds Water?
Why the water stays in
A bucket with holes would leak at once, so the riddle sounds impossible. A sponge gets away with it because its holes are tiny and joined together. Water clings to the walls of such narrow spaces and pulls on the water beside it. That pull is called capillary action, the same force that draws water up a paper towel, and in a small pore it can win against gravity. A soaked sponge therefore keeps most of its water until it is squeezed.
A sponge that is an animal
Sea sponges are animals. They belong to the group Porifera, a Latin name meaning pore-bearing. A sponge stays fixed to the sea floor and pumps water through its pores, filtering out bits of food as the water passes. It has no brain, no stomach and no true organs, which makes it one of the simplest animals alive.
The one at the kitchen sink
Most sponges sold for dishes are not from the sea. They are made of cellulose or foam, with holes formed on purpose. Natural sponges are still sold, and their soft skeleton is built from a protein fiber called spongin.
Making the riddle your own
This is an easy riddle to try with a real sponge. Ask the question, then press a wet sponge over a bowl and let the group watch the water come out, which turns the paradox into something everyone can see.