Jolie had cut herself that day and we veered into a conversation about how wounds heal.

“I know, Daddy!,” she exclaimed. “We can see how cuts heal with different things like Band-Aids, gauze, cream and stuff.”

A science fair project on cuts means someone has to get cut.

“Uh, Jolie, who are you going to cut?”

“You, Daddy.”

So, a couple of weeks later I sat shirtless as Jolie swabbed my bicep with alcohol and picked up one of the sterile, very sharp lancets I use for blood-sugar checks. She looked at the lancet, looked at me, looked at the lancet and ran out of the room. “I can’t do it, Daddy.”

Next up, Mom took the lancet and scratched my skin, hard enough, maybe, to sooth a mosquito bite but not hard enough to draw blood. “I can’t do it, Neil.”

It was apparently up to me.

I took the lancet, jabbed it into my bicep, pulled — skin makes an interesting ripping sound when it’s torn — and watched blood flow down my arm.

Then I did it five more times.

We photographed my wounds, applied various nostrums and bandages and took pictures. For a week, Jolie chronicled their healing with notes and pictures while I had fun telling friends about the project, rolling up my sleeves to display my stigmata and waiting for their horrified responses.

As usual, we left the assembly until the night before the project was due. After a cavalcade of mini-crises — research left at school, pictures that didn’t show the cuts and a late-night run to the drug store to develop better photos — Jolie put together the display all by herself. (Yup, that’s our story and we’re sticking to it.)

This time we made sure to mount one picture a little cockeyed so it wouldn’t look too grown-up. She lost five points for the error.

Jolie went to the regionals nevertheless. Her face fell briefly when she wasn’t among the winners, but she perked up as a flock of kids gathered around.

“That was your project?”

“The one with the blood?”

“He did it himself?”

“Ewwwww, gross!”

After we got home, Jolie handed me a note.

“Dear DaDa: I hope your arms don’t hurt too much. You were very brave giving yourself the cuts. Thanks for being my science fair guinea pig.”

Jolie is in high school now, more interested in boys, music and makeup than science fairs, and for several years I’ve gone unpoked and unprodded.

But the day came when her sister Aleeza brought home a flier from fourth grade.

It was science fair time again. But now it’s called an “invention convention” and involves creating an “invention,” some device that in a child’s view will make the world a better place.

For her first go, Aleeza decided to build a magnetic-levitation hover board. For her second, she constructed an auto alarm that administers a shock instead of sounding a siren.

So far, I’ve gotten off easy. The only bodily fluids I’ve donated to Aleeza’s cause were from a cut caused by an errant X-Acto knife.

But I’m worried about next year.

Neil Reisner teaches journalism at Florida International University.