One of my jobs in the Army is to give service members and their families tours of the demilitarized zone in South Korea. Before taking people to a lookout point to view North Korea, we warn visitors to watch their heads climbing the stairs, as there is a low overhang. The tour guide, first to the top, gets to see how many people have not heeded his advice.
On one tour I watched almost an entire unit hit their heads one after another as they came up the stairs. Curious, I asked their commander what unit they were from.
"Military intelligence," he replied.