Maddy's around 16 months now. She has a tendency to repeat certain actions around 10x, as if she was practicing to get it right. One time, she would keep opening the door to her playpen, enter inside, close the door, open it again, step out, and repeat!
Or she would open and close doors, as if to see how they work. Or sit down and lift herself up using the pack and play rail on a cycle.
It's really interesting to observe them doing this, showing how their mind works, and how they're struggling to perfect a task or simple activity, committing it to muscle memory or such.