Science explains everything, right? Well not all the time. Here are five examples of phenomenons scientists still can’t explain.

1. The Taos Hum

In Taos, a small town in New Mexico, residents are becoming annoyed with a low frequency hum in the desert air. Surprisingly, only about 2% of residents report hearing the sound. No one has been able to locate the origin of this sound. Some call it supernatural and others believe it is manifestation of tinnitus, or ringing of the ears.

2. Deja Vu

Deja vu is a French term that describes the feeling that someone has experienced the same situation before. Multiple studies have been conducted to find out why we have this feeling. One particular study put people in a virtual computer world and found that deja vu was triggered most when a person visits a place that was similar in layout to a previous place, but not consciously recognized. Deja vu could come from experiencing the simultaneous sense of newness and oldness. Another study has shown a patient has felt deja vu after taking two drugs to ward off the flu. Deja vu might come about when the brain improperly encodes a new memory, or when it misfires when establishing a sense of familiarity.

3. UFOs

UFOs, unidentified flying objects, are far from new. People across the world report a sighting, but NASA, air traffic control, or the military claim it as theirs. One specific encounter from 2004 is still unexplained. On November 14, 2004, the aircraft carrier USS Nimitz noted an unknown craft on radar 100 miles off the coast of San Diego. For two weeks, the crew had been tracking objects that appeared at 80,000 feet and then plummeted to hover right above the Pacific Ocean.The tic tac shaped object had no visible markings indicating windows, engine, or wings. Even the fighter jets infrared technology did not detect any exhaust coming out of the object. The water would boil where the object hovered over and fly away as soon as the fighter jets approached it. The craft moved three times the speed of sound and twice the speed of the fighter jets.

4. Yawning

No one knows for certain why yawning occurs, but there are some suspected purposes. One idea is that yawning cools the brain by increasing blood flow to the jaw, neck and sinuses. Another theory is that yawning is an alert our bodies gives to stay awake. This makes sense because we yawn when we’re tired. However, no one knows why yawning is contagious. People tend to yawn when others around them do, or even yawn when they see the word. Did you yawn while reading this?

5. Bigfoot

To some this is the funniest phenomena, but others wholeheartedly believe in it. Bigfoot, a manlike beast, has been photographed throughout the forests across America.  Not a single beast has been caught by a hunter, hit by a car, or even died of natural causes. Since there is no evidence of teeth, bones, or even its hair, it is impossible to prove this universal negative.