What's the difference?

I know that Andy and Doug are aware that they are twins. They volunteer the information when introducing themselves to new people.
At church this last week a girl, who was probably in about 4th grade, was visiting with a friend who goes to our church.
Now Andy and Doug barely look like siblings, but I realize that sometimes people lump them together anyway.
I overheard the girl ask Andy how she could tell them apart.
Andy said,"I wear long pants most of the time."

And truthfully...Andy does like to wear long pants most of the time. It's just not the characteristic I would have pointed out to someone.