TSA pulled my bags out for additional inspection once because I pulled them across my father-in-law’s lawn right after he had fertilized it and the sensor tagged them for the presence of explosives.
After an attack or coming back into the Green Zone we would first go to the wash rack & hose off the vehicles. We were known to set off detectors from time to time...residue was all over the place.
A co-worker of mine had that happen to her. She'd dragged her bag across the grass of hotel she'd stayed in and it picked up the residue.
She missed her flight and was not happy.