I remember that adults were capable both of whistling and of blowing up balloons, two skills which baffled and frustrated me as a child.  

 I remember that when my father used to do comic fake phone conversations when I was 7 or 8 years old, he'd always end the "conversation" by saying, "Okay, bye."  And I was surprised by that formulation -- not the bye, but the "Okay."  So I would try to do the same sort of fake conversation and noticed that I always said "okay" before "bye," and then noticed that I always said it in real phone conversations too, and that it was almost impossible not to.  That was really interesting.

 I remember being delighted when I learned that you could open our kitchen garbage can by pressing down on the foot-pedal.  I think it was a new one, but I'd seen the foot-pedal on the kitchen garbage cans at both my grandmothers' houses.  I never used them, though, so the pedals just seemed like some old person's variation of our own garbage can, which I think didn't have a pedal.  but then we got a new one -- strangely like the old people's -- and stepping on the pedal raised the lid!  That was really neat.

 I remember the first time I put my thumb over the spout of a garden hose, thinking either that I could stop the water running or that I could reduce it to a trickle.  I remember how surprised I was -- and then a beat or two later delight -- that the water spurted out in a powerful jet.  For a little while this was esoteric knowledge, or so I thought.  I imagined my friends didn't know that you could squirt a hose that way.  But of course they came to the same realization at about the same time.  And now we'd all reached a stage of greater worldliness and competence.