I am currently learning about relativity of simultaneity right now, and I feel like this is a common phenomena that we experience every day (question at end). The example from Fundamentals of Physics by Halliday, Walker, and Resnick is as follows: "Suppose that one observer (Sam) notes that two independent events (event Red and event Blue) occur at the same time. Suppose also that another observer (Sally), who is moving at a constant velocity v with respect to Sam, also records these same two events. Will Sally also find that they occur at the same time?" Here is a picture of the problem below in which the two observers are Sam and Sally:
The answer to this question is that Sally will find that these two events do NOT occur at the same time. In a different scenario, instead of a light pulse being released as a result of the event occurring, a sound wave is released. Wouldn't Sam and Sally still record the same results as in the example above? What makes simultaneity so different in special relativity?