The Conscientious Lizard is an in-game achievement in Run 3. Despite the name, you don't need to use the Lizard. In fact, all characters are allowed except the Child.This achievement requires you to complete Level 40 without dislodging any tiles.
This achievement is hard for beginners. The crumbling tiles are spread all over the place, so it's really easy to touch them. To get the achievement, you'll have to figure out the best path to take.