In English, intonation is not part of a word's pronunciation. For example, "mom" and "mom!" are both valid pronunciations of mom. However, in the Chinese language, intonation (tone) is part of a word's pronunciation. For example, 妈 (mā, pronounced mah) means mother, but 骂 (mà, pronounced mah!) means to curse. There are a few interesting things to think about related to this fact about the Chinese language.
In English, a sentence can be turned from a statement into a question just by changing the intonation of the words. Try saying "this is mine" and "this is mine?" out loud. For the latter, you probably pronounced "mine" with an upwards tone. Can the same be done in Chinese, given that changing the tone of a word could change its meaning entirely?
Based on my experience speaking Chinese, it is possible because there are some words in Chinese that mean the same thing irregardless of the tone in which they are pronounced. In fact, these words often don't mean anything specific at all, because they serve as filler words that can be spoken with different tones in order to achieve the desired effect. For example, the Chinese translation of "this is mine" is "这是我的". The last word, 的, acts like a filler word, and can be said with an upwards intonation to convey the sentence as a question. Sometimes the last word in a Chinese sentence isn't a filler word, in which case a question word needs to be added to make the sentence question-able. For example, "he is running" is "他在跑步", but "he is running?" is "他在跑步吗?". The question word 吗 needs to be added because 步 cannot be pronounced with an upwards intonation.
It is curious that the way to express a question is the same between the two languages (upwards intonation). I wonder if there are languages for which this is not the case. Or, if varying the intonation of a word to indicate a question is not actually part of the Chinese language, but only something that native English speakers do when speaking Chinese.
As a preface, I know close to nothing about music theory so the following is all speculation.
Music contains intonations. Singing along to music sounds the best when the intonation of your words matches the intonation of the music. This presents a problem for Chinese songs: what do you do if the intonation of the lyrics don't match the intonation of the background music? I've noticed that a lot of modern Chinese songs sound off to me, and suspect that this dissonance is the reason. On the other hand, Chinese songs that sound extermely harmonious may be that way because the lyrics were chosen (either purposefully or accidentally) to match the tone of the music.