EMF

When exposed to strong magnetic fields, these crystals can rotate at about 60 times per second. When the crystals are attached to cell membranes, their rotation could contribute to abnormal cell physiology. This may cause some type of cell reaction in the brain that causes our conscience to see ghosts. Many things can cause magnetic fields like power lines and microwave ovens, but if the earths magnetic field somehow energizes the spirit energy to enable it to manifest itself into an apparition that can be physically seen, then its possible that it causes the crystals in our cells to react so that we can see them. So if all the elements are right, There is a spirit present, there is a strong magnetic field and the magnetite crystals in your brain cells just happen to be affected by it, then this may be why you see the ghost.