Because people don't use sound to convey information, if sound doesn't walk as fast as people, people will of course express their information by gestures or direct contact with people who need to be told. Sound signals lose their meaning, and language will not be created from the beginning. Even if there is language, people can't walk around when they speak, otherwise the tone changes greatly, and people's language may "omit" the tone and the timbre will not work. Only the loudness of the sound can be distinguished. Isn't that a simple language? It is too difficult to express too much semantics, or people have not expressed rich meanings, so the human brain will not develop and evolve well, because the human brain will not. Even humans still rule the world, but today's planes are not. Noisy objects don't move fast, and they are struggling or disturbed by the huge sound wave vibration that they don't want to leave, just like supersonic planes overcome the sound barrier generated by their own voices and hinder or interfere with their movement. Or, more importantly, nothing is moving fast. It seems heavy. Why? Slow sound propagation means that particles that propagate vibration have great inertia, so all objects should have great inertia. According to this, all life movements will slow down, and the life span of people and all living things will be longer, but all life will be longer and all movements will be slower. Maybe people's feelings will be no different from the real situation now. According to the universality of inertia, sound is still much faster than motion and language may still exist. This is the same as the theory of relativity that in the inertial system of high-speed movement, all movements slow down and life is prolonged, but people feel nothing abnormal. Only in the non-high-speed inertial system, observing the high-speed inertial system will feel abnormal. Haha, the detailed discussion depends on how slow you assume the action is, and whether you admit to extending the great inertia shown by the slow voice to the general.

Perhaps people, like fireflies, have evolved "light language" and replaced language with light signals. Then, people will have eyes to receive light signals and "light mouths" to send out light signals around their bodies. If there are no "ears" around to receive language signals, people will collide as easily as in today's society, but people will be very resistant to collision, and collision with each other has become a common occurrence. Haha, this is also very interesting.