Military bath

The kids were taking a bath together, and they had been in there a long time. I had given them a cup with baking soda in it and another one with vinegar. That kept them busy for over an hour, didn't even cost a dollar, and they might have even cleaned the tub by accident. I heard all kinds of splashing, spitting, and giggling, and I went in to check on them. The shower curtain was closed, and they must have heard me come in, because Sarah yelled, "Mom, you do NOT want to look behind this curtain!" I agreed that I probably didn't want to, so I didn't. But I did stay nearby and listen. I heard Sarah say, "Noah, if a soldier crosses that perimeter, you spit at him!" How does my little girl know about soldiers and perimeters?