Boo has a very long attention span. That would be a euphemism for "obssessive." This kid has been fascinated with elevators and sliding doors since he was about 18 months old. He also loves garage doors. Though still fascinated by the plain ole residential kind, he has now moved on to fire stations. He realizes how much more variety there are to them. He will just stand there, stare at the gears and tracks and ask how it operates, who operates it, how fast it is, is it bigger than so-and-so, compare the window pattern to others he's seen, etc. etc.
So it's mechanical things he's interested in: vacuums, lawn mowers, snow blowers and construction equipment. All this is a preamble to the fact that today, something clicked with him. Although he's had his Tinker Toys for years, he's finally "got" it. Don't you love it when you see a light come on in your child?
Here he is with his vacuum cleaner.