To some observers, it looked like an ordinary grilled cheese sandwich. But to the Miami woman who put it up for sale on eBay, and to some people who viewed it, there was an image of the Virgin Mary seared on this seemingly run-of-the-mill snack.

The psychological phenomenon that causes some people to see or hear a vague or random image or sound as something significant is known as pareidolia (par-i-DOH-lee-a).

The Rorschach inkblot test uses pareidolia in an attempt to gain insight into a person's mental state. (Image credit: Public domain)

The word is derived from the Greek words para, meaning something faulty, wrong, instead of, and the noun eidōlon, meaning image, form or shape. Pareidolia is a type of apophenia, which is a more generalized term for seeing patterns in random data.

Some common examples are seeing a likeness of Jesus in the clouds or an image of a man on the surface of the moon.

Famous examples of pareidolia

A prime example of pareidolia and its connection to religious images is the Shroud of Turin, a cloth bearing the image of a man — which some believe to be Jesus — who appears to have suffered trauma consistent with crucifixion. The negative image was first observed in 1898, on the reverse photographic plate of amateur photographer Secondo Pia, who was allowed to photograph it while it was being exhibited in the Turin Cathedral.

Many say this stump in Rathkaele, Ireland, resembles the Virgin Mary. (Image credit: BBC

Some visitors to St. Mary's in Rathkaele, Ireland, say a tree stump outside of the church bears a silhouette of the Virgin Mary.

Damage to the Pedra da Gávea, an enormous rock outside Rio de Janeiro, Brazil, created an impression that many interpret as a human face.

Many people thought images taken in 1976 by the Viking 1 mission showed a face on Mars that could have been the remnants of an ancient civilization. [Gallery: Mars Illusion Photos: The 'Face on Mars' and Other Martian Tricks]

In September 1969, conspiracy theorists claimed some Beatles records contained clues to Paul McCartney's supposed death. Many heard the words "Paul is dead," when the song "Strawberry Fields Forever" was played backwards, a process known as backmasking. This is a common urban legend often repeated to this day.

In 1977, the appearance of Jesus Christ on a flour tortilla set the international standard for miracle sightings. It happened in the small town of Lake Arthur, New Mexico, 40 minutes south of Roswell.

Diane Duyser of Miami sold a 10-year-old grilled cheese sandwich, which she said bore the image of Jesus, for $28,000 on eBay in 2004.

In 2004, Steve Cragg, youth director at Memorial Drive United Methodist Church in Houston, Texas, discovered a Cheeto that looked like Jesus.

Donna Lee of Toledo, Ohio, saw an image of Jesus on a pierogi she was preparing on Palm Sunday in 2005.

In 2007 in Singapore, a callus on a tree resembled a monkey, leading believers to pay homage to the "Monkey god."

An example of pareidolia: a cinnamon bun with the likeness of Mother Teresa. (Image credit: The Telegraph

A cinnamon bun bearing a likeness of Mother Teresa was first discovered at the Bongo Java Café in Belmont, Tenn. It was on display for about 10 years, until it was stolen on Christmas day in 2007.

In 2012, many people made a pilgrimage to a tree at 60th Street and Bergenline Avenue in West New York, N.J., to see a scar on the tree that some believed looked like the image of the Our Lady of Guadalupe depiction of the Virgin Mary.

Why pareidolia happens

There are a number of theories as to the cause of this phenomenon. Experts say pareidolia provides a psychological determination for many delusions that involve the senses. They believe pareidolia could be behind numerous sightings of UFOs, Elvis and the Loch Ness Monster and the hearing of disturbing messages on records when they are played backwards.

Pareidolia often has religious overtones. A study in Finland found that people who are religious or believe strongly in the supernatural are more likely to see faces in lifeless objects and landscapes.

Carl Sagan, the American cosmologist and author, made the case that pareidolia was a survival tool. In his 1995 book, "The Demon-Haunted World – Science as a Candle in the Dark," he argued that this ability to recognize faces from a distance or in poor visibility was an important survival technique. While this instinct enables humans to instantly judge whether an oncoming person is a friend or foe, Sagan noted that it could result in some misinterpretation of random images or patterns of light and shade as being faces.

Leonardo da Vinci wrote about pareidolia as an artistic device. "If you look at any walls spotted with various stains or with a mixture of different kinds of stones, if you are about to invent some scene you will be able to see in it a resemblance to various different landscapes adorned with mountains, rivers, rocks, trees, plains, wide valleys, and various groups of hills," he wrote in a passage in one of his extensive notebooks.

Sometimes artists use this phenomenon to their advantage by embedding hidden images in their work. Observers often view other objects in Georgia O'Keeffe's flower paintings, for example.

In 1971, the Latvian writer and intellectual Konstantīns Raudive detailed what he believed was the discovery of electronic voice phenomenon (EVP). EVP has been described as "auditory pareidolia." The allegations of hidden messages in popular music have also been described as auditory pareidolia.

The Rorschach inkblot test uses pareidolia in an attempt to gain insight into a person's mental state. Since the cards have been designed without any specific image in mind, this is an example of "directed pareidolia."