The Science of stabbing a potato
If you try to push or "twist" a drinking straw into a potato, the straw will simply bend or crush as it is not very strong.
However, as you can see here, if you stab quickly, the straw will go in quite easily.
This is because when you stab you are pushing right along the length of the straw (which is almost impossible to do if you do it slowly). In this direction, the straw is quite rigid and so it does not have a chance to bend before the sharp edges at the bottom of the straw have cut into the potato.
If you are going to try this yourself be very careful not to stab your own hand! You will see in the video that Heward has cut a straw in half - that makes it easier to control where you stab the straw and so it is safer.