The answer is: ko duck eggs.

Explanation: a duck egg test, which is a witty self-deprecating joke. A big circle drawn by the teacher. Generally said to have a "big zero egg", the exam test duck eggs can not be broken, not cooked, and even more can not eat.

Then there are few goose eggs on the market, goose eggs are very big. In geese and ducks and chickens to duck eggs and eggs are most common in life. Duck eggs are relatively large, in appearance more in line with the appearance of 0, with "big duck eggs" to correspond to the witty "big zero eggs".

Brain teaser solution ideas:

Brain teaser can not be used to solve the conventional thinking, such as: what animal's ass killing power than the mouth.

The answer is a wasp, because wasps are also known as "hornets", "ant bees" or "hornets". It hides a degraded oviduct at the end of its abdomen, which is a poisonous wasp needle. In the event of an attack or unfriendly interference, the swarm will attack, can cause allergic reactions and toxic reactions, serious cases can lead to death.