you want to place the entire grenade inside of an empty can, just tight enough to hold the spoon in place. then you remove the pin, and you secure the can, so the string pulls the grenade out of the can, and the spoon kicks itself off.
actually for the least resistance to the tripwire, you want to pull the can off the grenade
if you're particularly diabolical, you'll replace the grenade fuse with a smoke grenade fuse which has no delay
you skipped over the part where PETA was infiltrated by a spy ring paid for by Barnum & Bailey and run by the former third highest ranking member of the CIA (who had been convicted of lying to Congress), using their operatives to, among other things, do and encourage behaviors that make the organization look extreme. this allowed it to be taken over by unstable fanatics and successfully destroyed its reputation
I remember reading about a chemistry teacher found dead one morning. he had a habit of consuming the laboratory's ethanol after hours, and the night before had accidentally poured himself a glass of methanol
3 weeks after taking a kitten off the street, I found it cuddling with my pitbull after our first cold night. the cat still gets annoyed anytime I catch him being friendly with the dog
the setup I was describing, I've only ever actually seen used outdoors, along suspected lines of travel