Kids eventually outgrow childhood tales of Easter bunnies and fazura lucahSanta Claus. Sometimes, parents have to tell them. Sometimes, school friends spoil the mystery. And sometimes, the kids use logical reasoning to figure it out for themselves.

Fahd Ahmad wrote about how his son figured out the tooth fairy isn't real: an experiment. In his tweet, he detailed how his 9-year-old son came to that conclusion.

This Tweet is currently unavailable. It might be loading or has been removed.

"He's an inquisitive kid, thinking his own thoughts," Ahmad said in a phone interview. "He's got sort of a scientific mindset naturally."

Ahmad suspected that his son was skeptical of the tooth fairy, since he's already lost a majority of his baby teeth. The 9-year-old mentioned that he had a loose tooth, but since it "wasn't a tooth you'd see normally" like an incisor or a canine, his parents didn't notice that it was missing. When his tooth fell out two weeks ago, he didn't tell his parents -- opting to wait for the tooth fairy to take it from under the pillow herself.

"Normally I would ask about it, but I didn't really push him," Ahmad said.

After three days of waiting for the tooth fairy, Ahmad's son finally told his parents that his tooth had finally fallen out. That night, Ahmad snuck "a dollar or two" under his son's pillow in exchange for the lost tooth.

When Ahmad asked if the tooth fairy stopped by, his son said yes but didn't say anything about his experiment.

Two weeks later, Ahmad's son admitted that it was all a test. Ahmad wasn't there, but his wife confirmed his son's theory: the tooth fairy isn't real.

This Tweet is currently unavailable. It might be loading or has been removed.

Ahmad is a doctor and researcher who blogs about parenting and faith. Since he's Muslim and his wife is Christian, he frequently writes about raising children in a biracial, bi-religious home. Although his oldest son also identifies as Muslim, Ahmad's three kids still believe in Santa and the Easter bunny.

"While he doesn't actually view himself as Christian in a traditional sense," Ahmad said, "He still views those traditions as his."

But after debunking the tooth fairy, Ahmad's not sure if his son's belief in Old Saint Nick will hold up.

“I think he’s mostly wanted to believe,” the doctor reasoned.

This Tweet is currently unavailable. It might be loading or has been removed.

As a doctor, Ahmad says he tries to approach conversations with his kids with some level of logic, but also credits his son's school for encouraging him to "think through some problems on his own."

Problems including disproving the tooth fairy, apparently.

This Tweet is currently unavailable. It might be loading or has been removed.

As thoughtful as his son's experiment was, though, Ahmad pointed out one flaw: “I think he lost his future cash flow, which is something he probably didn’t anticipate.”