When the app starts, press to move over to ‘Library’ and select ‘Interactive Episodes’.
This is unlocked in Episode 2, ‘Baby Bear’s Baby Doll’, Chapter 5, ‘Ring Bells with Ernie’.
When Ernie tells you to jump up after he places a bell on the hook, jump until it makes a sound. You have to do this three times.
The simplest way to unlock this achievement is using ‘Chapter Select’ to choose the chapter. When the chapter is over and the next one starts, just press , move over to ‘Stop’ and press again. The achievement will unlock when it is buffering. You can alternatively watch the entire episode, but that would be more time consuming.