Late on Christmas Eve a boy boards a mysterious train that waits for him: the Polar Express, bound for the North Pole. When he arrives there, Santa offers him any gift he desires. The boy modestly asks for one bell from the reindeer's harness.
It turns out to be a very special gift, for only believers in Santa can hear it ring.
Take a look here: https://www.youtube.com/watch?v=8VozCDstf8c