my doc figures I got that from my days in Nam, pushing over trees that were full of defoliant(agent orange)
PUSHING over trees? .. I did some of that when I was first in-country with a D-9 up and around Tay Ninh. Most of the heavy equipemnt work I did was on a grader though.
THEN I was a helicopter crew-member in and around the Delta and Plain-of-Reeds ...we flew air-cover for the River Rats on many occasions and flew-through AO many times.