You know the old story. A feeble looking old duffer touches a young, fit, agile, mobile and hostile looking thug and the thug drops like a flying grand piano. Is this magic? Is there any truth in this apocryphal story? What's going on here?
Death touch is real but not what most people think it is. To hit in this way you have to get a whole list of techniques correct. Each bullet point on the list does not add but rather multiplies the force generated. For example, one thing on the list is the correct use of body mass to strike. Another thing on the list is use of the smallest contact area to hit (for example the point of your finger). Doing both of these two things together multiplies the force generated i.e. the result is much, much greater than the sum of the parts. When you can put together all the things on the long list, you're doing death touch. You can utilise Chinese medicine theory to analyse what you're doing and how to put combinations of strikes together to again, have multiplied effects. This is fun and insightful but not really necessary as your body and the forms you use naturally do this for you. In any event you usually don't have time to do this ("Hang on while I figure out a counter as I've got to check on the time to sort out which meridian point to hit and, by the way, I also have to compensate for Eastern Standard Time"). So, the old man is actually doing a raft of things that outside observers are just not picking up. The movement he's using is optimised so that his motion is complex but minimal (very, very small spirals!).