Isn't it crazy how little ones seem to learn piles of new things overnight? They can go weeks, just coasting along, not showing that they have picked up new info and skills.... and then BAM! It's like they had an IV infusion of brain cells while they slept.
My little guy just turned three last week and he had really slowed down on his aquisition of new info/skills. It's like he took a summer vacation along with his sister and focused on playing hard. In just this past week he now counts everything (there are 18 chairs in our ophthalmalogist's waiting room, in case you are interested :-), he read numerous words in his books (same words in a few different books), completely potty trained himself and gave his preschool teacher a long and drawn out lecture about the differences between steam trains and diesel trains (he could barely talk 4 months ago).
I think this is why I so often question whether my children are really GT. They seem so 'normal' and fit in so well with their age-mates 90% of the time. It is these spurts of growth in their knowledge that bowl me over every now and then. After speaking with some of the other moms at his school, I realize I need to spend more time with other kids his age because my sense of a normal three year old must be warped, LOL!