LONDON • It’s a weekend warrior’s nightmare. You’re playing hoops in the driveway and go up for a lay-up. You land and hear a pop: you’ve torn your Achilles tendon. Do you have surgery or hope it ...

You grab an avocado, take a knife, and begin slicing it in your hand—it seems pretty standard, right? This method is all wrong and could actually be dangerous. In fact, one in four people go to the ...