This is essentially a story-based achievement. You cannot progress in the game without obtaining it.
About halfway through level 4, you will be prompted to press
to latch onto one of the tongue rings in the background. The achievement will unlock the second you latch onto that.
As near as I can tell, you cannot obtain this achievement before Level 4! There are no backgrounds to enter before then. Somebody correct me if I am wrong, but I have been checking the backgrounds on the 1st level, and there is nothing (there are no backgrounds on level 2 and 3 due to them not being sidescrollers)
If you are downvoting, I would be interested to know as to why so I can improve the solution. However, I really can't go much beyond "you are guaranteed it in level 4"