In the Mountain level, at around 49% into the game, you'll come to a section just after a lift with a bunch of extremely long freaky legs resembling a forest of Peter Crouches. Roll the orb close to the legs to make them retract and disappear. There are 8 before the next checkpoint, 6 out in the open and 2 up a slightly hidden path off the top of the screen, which will also lead to the secret mural for this level as well. A two for one solution, you lucky thing.
There are a further 2 legs (for a total of 10) following the aforementioned checkpoint that form part of the next puzzle,
however I'm unsure if these actually count towards the achievement, let me know in the comments (I backtracked as I missed the 2 up the hidden path in the previous section, which is where this achievement unlocked for me). and thanks to FusionDragon28 for confirming in the comments that these two do in fact count, thus you are looking to disturb all 10 legs.