I found this video on YouTube providing instructions for tying a crab claw lanyard. Nothing wrong with it in the context in which it is presented. He mentions moving ACROSS a via ferrata and there is footage in the video showing people moving horizontally on cables. But an important caution needs to be added because there are via ferratas that also involve moving UP.

See the illustrations from Petzl below the video. When moving UP on a via ferrata, there is a risk of fall factor greater than 2, in which case you need to have a lanyard that provides for energy absorption.