Investigate, Inspection, Investigation
If a tree is growing out of a top hat you need to inspect it to find out why and how this happened. You should probably investigate the area too. I mean, how could a tree grow out of a top hat anyway? Seems suspicious.
In the middle of your inspection you realize you need to saw (さ) the tree open to come to a good conclusion. This seems a bit unnecessary, but no! No! For the sake of this investigation you must saw the tree in half!