Isn’t it incredible that for how advanced modern medicine is, we’ve essentially found something so complicated that the best we can do is poke around and see what happens?
It's a bit more sophisticated than that; she knows almost precisely what is going to happen, but the exact boundaries of the fluent brain that she's looking for are not clearly marked, and brain moves around a little; these are not solid-state circuits, so without this check you would have to err on the side of caution, which is contrary to the goal of removing as much tumor as possible. Probing ahead of where they're going to resect is a simple and effective solution.
