Terrifying trip on a tightrope!

It's a good job Helen Skelton didn't see this clip before she undertook her Sport Relief tightrope challenge.

This is highwire supremo Nik Wallenda walking 30 metres above the ground in America.

He was just coming to the end of his walk when he tripped!

The stumble gave everyone on the ground, including the commentator, quite a shock!