Interesting topic, nice wacky and/or clever ideas so far...
I am thinking it has to be used to perforate something that is clean and dry, because the wood is unstained and he must have used it before...surely
So based on this maybe the thing the device perforates, whatever material it might be, is used for one of these functions:
1) Uniformly planting something into the substrate so a nice plant carpet is achieved once grown a little? Is he into planted tanks?
2) Stopping a gravel substrate or similar from mixing with another substrate beneath it?
3) To create a plastic bottle based live food feeder, placed on the surface of the water in the tank?
Could anyone take these ideas further based on past experiences? I am new to the hobby so am only guessing with not much clue, I don't have a planted tank and I haven't feed live wriggling food to my fish
yet
Hope that helps
Edit: the fact that one of the main boards is longer than the other suggests to me that whatever goes into this thing is on a roll maybe, or at least quite long. So could this be how it is used:
1) One end of the "material" gets put in over the board with the holes and side pieces are pierced into it to hold it in place
2) It is perforated by placing the second board on top (as described in the pics before) and pushing down on it
3) The top board is removed to pull the nails out the same way they went in, but the "material" is still held in place by the side pieces
4) Side pieces are removed and the "material" is moved along and the process is repeated
That's it, no more ideas...this is a great brain teaser!