Almost eight months ago now, I was trying to finish the flooring in the nursery before the little guy came along. Sadly, that was not to be. These are cleat nails, driven through flooring using a pneumatic nailer. You can see a chunk of a row of nails, ready to go into the nailer, as well as a single nailhead in the tongue of the bamboo I was laying, on top of the red rosin paper I was using as an underlayment.
Three more boxes of flooring ready to get laid down. One of these is still unopened, the other is half-used as I finish the floor upstairs. Pierrette already had the closet organized:
Finally, a bamboo plank where you can see the tongue clearly, sitting on top of the red rosin paper: