Change Bulbs

Instead of going out to lunch, I eat carrots and celery at my desk at work.
Then, when I get my lunch break, I go for an hourlong power walk through the tunnels under Downtown Houston.
During one of my walks, a crew of three men had spread a tarp on the floor and were changing lightbulbs.
But they were moving the ladder out of the way when people approached, not rotating it as one guy on it held the bulb.
Why they had the tarp on the floor, I never asked. I just walked back to work and pondered.