You will need two pokey sticks - knitting needles are good - paper and pencil and a willing victim. The idea is to demonstrate the differing density of nerve endings over your body, and figure out the most sensitive parts (steady!)
Choose the area to work on - classics are the fingertips and the back, but legs, feet, toes, arms all are worth it. My little scientists got a bit carried away poking me with knitting needles, for some reason.
Touch the person with either one
or two points, held about a centimetre apart, and ask them to tell you how many points they feel.
I have only just realised what short stubby scientist fingers I have. Harumph.
Record how many times they get this right. We tried 4 times on each body part.
Once you figure out which areas are most and least sensitive you can vary the distance between the needles - if you put them 5 cm apart, can you now reliably distinguish one from two touches on your back?
You can make a little chart, and probably could get creative with graphs and so on.
There is a variation of this that has you running a pencil point slowly up your forearm and noting the places where it feels icy cold as you encounter a nerve ending, but I think mine need to be a bit bigger before we do this. I remember marking the points with felt tip pens and plotting them out when I was about 12. That explains a lot.
And now, though I love you all dearly I'm going to have to spend a little quality time with a glass of red, a bowl of butternut squash lasagne and James McAvoy ...