Logic.

When I was five, I liked to put talcum powder on my hands before I went to bed (why, I have no idea). I also liked to get myself a glass of water. The trouble was that if I put the powder on first, I'd get it wet when I filled my water glass. If I put the powder on second, I'd get powder in my water. I did the former, because I was worried that the powder might be poisonous. But one evening, I decided to live a little and do it the other way around.

But after I had been in bed for a few minutes, I was struck with terrible remorse. Oh god! It probably WAS poisonous. How could I have been such a fool? I wept. My father heard my stifled, choking sobs from the next room.

"Are you all right?" he called.

"Yes!" I said. "Fine! I was just coughing."

Then I got to work wondering how long poison could take to kill me. After all, I wasn't dead yet. How long would it be before I knew I was in the clear? I began to calculate. Right now I was in kindergarten. Next year, I would be six and in first grade. When I was seven, I would be in second grade. (Hey! If you subtract five from your age, you get the grade you're in! Clever!) Right. Probably if I was still alive by the time I started second grade, then, I could safely assume that the talcum powder had not, in fact, killed me.

The end.