Santa Inocencia (Saint Innocence) died 300 years ago, and her remains are preserved in a glass case at the Cathedral of Guadalajara in Jalisco in Mexico.
A visitor was filming a tour around the building on their phone when they captured what appears to be the corpse opening her eyes.
The startled tourist then posted the eerie moment on YouTube, which has since racked up over 1 million views.
At first glance the body, which has been preserved using wax, could easily be mistaken for a statue. But as the camera moves up and down her corpse and stops at her face, the dead girl seems to wake up for a brief second.
Unsurprisingly, many viewers have said the video is a fake, but others believe it may be a sign.
There are many varying accounts of how Saint Innocence met her demise.
The best-known version says the youngster was a Mexican girl who wanted to take First Communion with her classmates, but was forbidden by her father.
She was invited by the nuns at her school to take part, and when her dad found out what she’d done he stabbed her to death.
The locals then took her remains to the cathedral where she became a symbol of a child’s love for Christ.
Watch the horrifying clip below.