Dr's Casebook: A fun experiment to try out on Christmas Day

So here we are with Christmas Day almost upon us. After all those Christmas cards you have written, and the presents you have bought and wrapped, it will soon be time to sit down at the most festive meal of the year. The food that the chef has prepared is of course the centre-piece of the occasion, but don’t forget about the little extras that distinguish Christmas dinner from any other.

Dr Keith Souter writes: I am talking, of course, about the Christmas crackers and the little trinkets and jokes you find inside. Well, as hats are pulled on and the jokes read out you might like to try this little experiment around the table. It is based on a trick the ancient Romans used to play.

placeholder image — The effect is that you ask everyone to place their right hand on the table and raise a particular finger in response to questions you make up.

The effect is that you ask everyone to place their right hand on the table and raise a particular finger in response to questions you make up. Then, you ask a pointed question that needs a yes answer – perhaps who doesn’t want to do the washing up after the meal?

However, they will find that they cannot lift that designated finger up.

Ask them to place the hand as flat as they can on the table with the thumb and fingers spread out, except for the middle finger (between the forefinger and the ring finger) which should be curled under, with its knuckle resting on the table.

It depends upon the way you ask them to position their hand. Ask them to place the hand as flat as they can on the table with the thumb and fingers spread out, except for the middle finger (between the forefinger and the ring finger) which should be curled under, with its knuckle resting on the table.

Then ask questions and with the first tell them to raise their thumb if the answer is yes. Perhaps, are you having a good time? Ask another such as, have you liked your presents?

If so, raise the little finger. Then perhaps are you looking forward to the rest of the day? If so, raise the forefinger. And then the trick question about who doesn’t want to wash up? If the answer is yes, raise the ring finger. To their surprise they will not be able to do, or will only manage a millimetre or so.

The reason is an anatomical quirk. This is because the tendons that control the movements of the fingers are interconnected. The ring finger and the middle finger share a tendon, so with the middle finger curled under, the ring finger is locked.

Enjoy your Christmas meal.