If you have grandchildren, you know that one of the chief compensatory joys of getting older is time spent with them. Each visit gives you an opportunity to teach them something, to pass along some acquired wisdom, and to make up for the deficiencies in how you raised their parent.

The past comes back to us in mental snapshots. We tend to remember the pleasant things more readily than the unpleasant, when we remember anything at all. Or when we run across something that has emotional value.

I found a little manila envelope recently with a child's tooth in it. After a few moments of studying it, the way Louis Leakey might study a fossil from a pre-historic man, turning it in the light and examining it for telltale signs, I realized it was from my oldest son.

The tooth was saved because that's what we do with our children's teeth. They take on a value far beyond anything measurable.

Aided by the presence of the tooth, I remember the day it came out. And how it came out. My son presented himself in the upstairs master bedroom one morning to show us a loose tooth, his first. I told him I knew just what to do, which was to use the tried and true tooth removal system shown me by my father.

I guided the boy to the doorway where I tied a stout string to the door knob. The other end I looped around his loose tooth. He was a bit wide-eyed at this point. I asked him to back up to put a belly in the string, then I threw the door shut the way my dad showed me. Out came the tooth, along with a little blood.

By coincidence, I called that same boy, now a man with a wife and three children, and heard that one of the grandkids had a dangler of her own and was wandering around the house exhibiting it.

I reminded him of how I took out his own tooth. I could almost hear him wince on the phone. He said he would just let nature take it's course with his daughter's tooth.

Sure enough, a week later, out came the tooth.

The family had just moved to a new house the weekend the tooth got loose. I helped (by barbecuing and making humorous remarks) and also counseled my granddaughter on dealing with the Tooth Fairy.

"How much do you expect to get for that tooth from the Tooth Fairy when it comes out?" I asked her in all earnestness.

"Five dollars," she said just as earnestly.

I glanced with arched eyebrow at her father, who gave a resigned shrug and bit into a hot dog.

"Does the Tooth Fairy know you moved? What if she can't find the new place?" I asked her.

She gave me a puzzled look. Then said, "Will you call her on your cell phone and tell her our new address?"

I figured she was kidding because I was.

She wasn't.

When I didn't begin dialing immediately, she said, "You have to call her now so she knows we moved."

I understand badgering. I'm married. So I dialed the Tooth Fairy. I got her answering machine but left a detailed message, including location of the bedroom in the new house and which pillow to put the money under.

The little girl with the missing tooth went to sleep that night fully expecting to find that the Tooth Fairy had visited in the night. When she awakened, brimming with anticipation, she turned over her pillow and found...nothing. She was very worried.

She ran into her parent's bedroom, where they were still rolled up like burritos in the covers, and announced that the Toothy Fairy had obviously forgotten to show up. Or, and this was the more likely explanation, she had not been able to find the new place. Maybe she hadn't checked her answering machine? Maybe she just got lost?

But no. That could not have happened because the Tooth Fairy had been at this house, the new house, before, when a boy named Jeffrey lived there. She knew the place, alright.

Her father, my son, assured her they would get to the bottom of this. And he did.

I heard the whole story on the phone on Saturday afternoon, from the girl with the missing tooth, sounding quite lispy. The Tooth Fairy came through Friday night, after apparently having gone to the old house first and, discovering her mistake, checked her answering machine. That mistake cost her five bucks.