Why do peoples nose run when I eat

When they eat? When you eat?
Are you referring to very elderly people specifically?

My mom's nose has always run when she eats ice cream. Now she's 91 and it runs every time she eats anything. About a month ago, her doctor sent her to a hospital for nasal and throat tests of various kinds, but no problem was found. Thus, tests can be run if the nose running is bothersome or the color of the discharge is cause for concern. My mother's doctor's solution for her was to tell her to always have tissues nearby.

Now, if peoples' noses run when YOU eat, something else is going on.

Darn it, Wondergirl, MY nose runs when I eat ice cream now!
I think I have a nerve from a tooth hitting inside my nostril. It feels that way.