"We need 4 more"

After he brushed his teeth, I told Collin that I needed to cut his finger nails.  He sat down on his stool and held one hand out.  He showed me the sharp pointer finger so I cut that nail first.  The same thing happened with the other hand.  I then gathered the nail clippings and put them in one of his hands.  He counted the clippings and said, "There are 6 and I have 10 fingers."  Not thinking he would know the answer but I thought I would ask anyway, I said "If you have 10 fingers and only 6 nail clippings, how many more are on the floor somewhere?"  He held out his other hand and, lifting one finger up at a time, he said, "7, 8, 9, 10.  Mommy, we need to find 4 more."  What!?!?!??!  My boy just did math.  I was so proud of him at that moment.  I did look around for the remaining clippings and did not find them....not really caring because Collin just did math.