Kaleb had stated to do commando style crawling to get around, and today looked like he was trying to lift his body up too. To help him practice, I got out two of his toys that move on their own.
One is a little eyore toy that slowly walks along a bit and then stops waiting for the child to follow it, moving again when the child touches it. The other toy was one my dad got him for Christmas - a little alien that moves in random directions until it hits something where it will change direction, eventually stopping somewhere, waiting to have its head bopped before it goes off again.
We had these two toys out, the eyore had moved along the floor but Kaleb wasn't following so it waited where it was. Meanwhile, the alien was zipping around the floor and eventually hit into the waiting eyore, which stated it off again - one toy had interacted with the other toy causing it to carry on moving.