Yes good question! Sometimes I make it sound like the answer was easy to find, but really it took us two years to figure out how to measure the force it takes to deform brain and compare it to the force it takes to deform jelly. The experiment was really difficult to realise in the lab, while meeting the standards of good science. For instance we had to make sure that the experiment could be reproduced and provide the same result over and over, by us or by other scientists. Once that worked, the maths were easy, pfew!
Then we decided to measure the speed of sound in the brain and in jelly, so that we would work on an entire intact brain instead of having to cut out a piece as in the previous experiments. That took another two years!