For six months nobody could figure out what was wrong with Khloe Russell after her left nostril started pouring with smelly green mucus.
Mother Katelyn Powell, from Hemet, California, was unable to explain it - as were the two doctors, an ear nose and throat specialist, and the dentist she took her daughter to see.
But one day while blowing her nose a 1.5 inch (3.8cm) safety pin popped out and Khloe was forced to admit the truth - she got the metal object stuck up there while playing, then "forgot" about it.
Katelyn said the problems started around September last year when Khloe's nose began to run uncontrollably.
Speaking to ABC 13, she said: "About six months ago, her nose just started [running] out of this one side. Green, green, green constantly and it stunk."
Katelyn said she took her daughter to a doctor who examined the offending nostril but couldn't find anything wrong, so assumed it was a sinus infection and sent her home with antibiotics.
After 10 days, with no success, Katelyn took her to another family doctor and an ear nose and throat specialist, who also failed to spot the pin, as it was wedged so far up her nose.
The panicked mother even took her daughter to the dentist, afraid that a problem with her teeth was causing the nasty discharge.
Despite repeated trips to the doctor, and various rounds of medication, Khloe insisted she didn't know what was wrong and said she felt no pain.
But the answer eventually came after the girl's uncle, Katelyn's brother, got her to blow her nose really hard and the pin popped out.
Khloe had been regularly blowing her nose before, but it was only on this occasion that the pin decided to make an appearance.
Confronted with the rusting metal object, Khloe admitted that she had tried putting the object up her nose while building a fairy castle by herself.
Katelyn added: "It was a huge object. It was bigger than her nose. We were horrified. I was like, 'Did you put this up there?' She did, but she forgot to tell me."
Katelyn says she doesn't blame the doctors for missing the pin, and is simply relieved the problem is finally solved.
She added that she has since had a conversation with her daughter about putting objects up her nose, and the girl has promised never to do it again.