Many countries follow special customs when a child's baby teeth fall out.Many of these customs tell stories about animals taking the teeth.

　　For example，Koreans have the custom of throwing the fallen tooth onto the roof of a house so that a magpie(喜鹊) can take the tooth away and bring a new tooth for the child.This custom is also followed by some other Asian countries，such as Japan and Vietnam.

　　Other countries，though，have tooth customs about other animals.In Mexico and Spain，for example，it is thought that a mouse takes a fallen tooth away and leaves some money.But in Mongolia，it is dogs that take children's teeth away.Dogs are highly respected in Mongolian culture.It is believed that the new tooth will grow strong if the baby tooth is fed to a dog，so parents in Mongolia will put their children's fallen teeth in a piece of meat and feed it to a dog.

　　In France and the USA，a child will put a fallen tooth under his or her pillow before going to bed.It is thought that in the early morning，when the child is still sleeping，the Tooth Fairy will take the tooth away and leave something else under the pillow.What she will leave is hard to know.It is said that in France the Tooth Fairy may leave some candies；however，in the United States，she may leave money.

阅读短文，回答下列问题

1．In Vietnam，if a child's tooth falls out，what will he or she do?

Throw it onto the roof of a house.

2．What's the main idea of this passage?

Customs about fallen teeth in different countries.