x-post from a Facebook comment
I am embarrassed to admit that I subconsciously know which parts of my 6-block walking commute have trees with low branches overhanging the sidewalk. I find myself cringing when I get near them, head buried in my phone reading some interesting blog post, because I've probably run into all of them before.

no subject
<--Is really short and rarely has to duck.
Of course, if I'm walking with someone tall I'm not really aware of where those branches are, so I don't warn people about them.