This gas is very harmful to the human body. Scientists say that the ancient sages and wise men knew about it and in order to warn the simple folks of those times, they invented the myth of evil spirits, residing on these trees. Thus, while resting at night, they are saved from the harmful effects of carbon-dioxide gas.
Using a horse for a journey was quite common in the past. A lost horse-shoe then meant that a limping horse could be found nearby or that there was a horseman with a horse that had lost a shoe somewhere near. It also indicated that a place of rest could be nearby. These could be the reasons why finding a horseshoe was considered lucky by the people.
Many of us consider the owl an unlucky bird. The scientific reason being that owls inhabit only in old, broken-down buildings. It also implies that the place is infested with rats which are the staple diet of the owls.
Hence, whenever an owl hooted, people knew that the place, they were resting under, was either old or infested with rats and was thus unsafe for living. Later on, this belief took a form of considering every owl hoot to be unlucky.
In India a white or an albino owl is considered lucky because people think it to be the vehicle of Laxmi, the goddess of wealth, while the black owl is considered unlucky because it is the vehicle of Yama, the god of death.
However, the reasons for the beliefs of considering number thirteen as inauspicious; or treating the black cat crossing the path or sneezing before someone leaves the house; or a howling dog unwelcome are lost in obscurity.
They are still being followed today without any reason. Even in European countries number 13 is considered so bad that in many hotels and offices rooms are numbered 12 A and 13 becomes 12 B.
The followers of these superstitions are both educated and uneducated. Their biggest clientage, of course, consists of ladies. No amount of scientific explanation can dissuade them to give up their favorite superstitions. It appears that there is no hope for the society to escape from their rigid shackles for many years to come.