i did the same thing with a couple (maybe 3) spools of thread that i strung across the street from mailbox to mailbox, not our mailbox either.
i just got a wild idea in my head one day and there wasnt anyone around watching me.i think i was eight.
the car drove through slowly and it actually stopped the car. !!
she gripped the steering wheel and peered harder through the windshield, seeing the strings.
she then stomped on the gas and drove through. they broke, and i hid.
never got in trouble thank goodness.
i hadnt ever given thought to someones head cutting off..holy moley!