I think that's a reference to back when they had chemical fuses, which weren't exactly known for their precise time keeping. Using a 4 second timer gets a lot more interesting when they can vary by a couple seconds. Makes me wonder how many guys had them go off in their hands, intending to cook off for a second or two before the throw to minimize toss back odds. Yikes. Supposedly we're going to laser ignition for grenades, which will be safer, more precise, and might allow for a grenade with multiple settings (Push 1 for Concussion, Push 2 for Fragmentation, etc).
Captante's post reminded me of a guy that was in the news not too long ago. Chinese clone of a potato masher, live one, and had been used for decades as a walnut smasher.
Found it: https://www.popularmechanics.com/military/weapons/a24544/hand-grenade-crack-nuts/
I'd have gone right out and loaded up on lottery tickets after that. Some luck.
Not as bad as the ruskie who was taking selfies of himself with a grenade with the pin pulled.
https://www.independent.co.uk/news/...ander-sasha-chechik-labinsk-pin-a8080771.html