The phenomenon of touching the dog's head and its ears flying is called the ear lift reflex, which is also known as the dog's airplane ear phenomenon.
In most dogs, the ear lift reflex is an instinctive response. When you touch your dog's head or touch its ears, your dog's ears may immediately lift upwards. This is because there is a set of muscles inside the dog's ears that, when stimulated, cause contractions, which cause the ears to move upwards.
The main reason for this phenomenon is protection and vigilance. The ancestors of wild animals and dogs often used the position and movements of their ears to express their emotions and level of vigilance. Therefore, a dog's ears are tucked up to help them hear their surroundings better, and they can communicate their emotions by changing the position of their ears.
In addition to protective and vigilant effects, the ear lift reflex may also be associated with genetic and individual differences in dogs. Some dogs may be more prone to reflexes when their ears are touched, while others may be less reactive.
All in all, the phenomenon of a dog's ears flying when touching his or her head is an instinctive reaction of the dog, which is related to both protection and vigilance, and may be related to genetics and individual differences.