A friend of mine is also freakishly afraid of snakes, or anything that would resemble one! She is even afraid of Northern Pike and Muskie, so you can imagine how bad she gets if she got one on her line while fishing.
Phobias, such as a fear of snakes called Ophidiophobia is not uncommon. It usually has to do with some kind of fear causing event when encountering a snake. But it can be easily overcome with some targeted therapy including desensitization. One can become fearful through general classical conditioning just out of innate inborn survival fear action in regards to the unknown. Such as running after someone with a snake for their first time seeing one.
