Here Benji, our budding engineer, tries to understand how wheels and, to a lesser extent, strollers, work.
A thorough exploration of all wheeled devices is required. He spends 10 minutes at a time spinning wheels.
Keys do hold some fascination, but really, nothing compared to wheeled objects.
Oh, I should also add that in the last day or so, Benji has also started pointing at things. Now he points at food he wants, buses, trucks, doggies, Daddy, and other less obvious targets.