https://mindlabkids.s3.ap-southeast-2.amazonaws.com/user/2/field_video/rich%20echoing%20question_1/rich%20echoing%20question_1__720.mp4
1 person
30 mins

When Viking Rich was out in the mountains one day, he shouted for help when he lost his way! But, instead of someone replying, he heard his own voice repeat what he shouted!
How does that work? And why does it only happen in some places?