This rattle-can trigger is certainly not reinventing the wheel, but it is a very comfortable, inexpensive and lightweight design that will come to the aid of anyone whose index finger has become permanently locked into an “L” after extended spraying (author raises misshappen hand). Like a good ratio rocker arm in reverse, the mechanical leverage is 2.5:1 for fatigue-free paint application, and it snaps onto any standard aerosol can with a push-and-twist motion. They’re available at Ace Hardware, Tractor Supply Co., and through Amazon.com.