More than meets the eye

As I was on my way to the grocery store, I noticed that I shared the sidewalk with a much slower walker... one that was just inching along.

A geometrid caterpillar (Geometridae) inching its way across the sidewalk.

I crouched down to watch this geometrid caterpillar, more commonly known as an inchworm, as it crossed the sidewalk.  However, other pedestrians, who seemed intent on ignoring both me and whatever I was looking at, nearly stepped on the caterpillar.  Therefore, I decided to aid the caterpillar in its journey and gingerly picked it up.  Suddenly, something unexpected happened: the caterpillar went rigid and transformed into a twig.

The same caterpillar doing an impressive imitation of a twig.

Or, at least, the caterpillar took on the appearance and texture of a twig -- which might have been very helpful for the caterpillar had I been a bird looking for its next meal.