The last word "chai" is the sound change of ancient and modern times, that is, the pronunciation of ancient and modern times is different.
Rhyme, depth, heart, gold and hairpin all belong to the Pingsheng invasion department.
It is not harmonious to read in modern Mandarin, but the ancient sounds preserved from dialects are very harmonious to read. For example, in Hakka dialect, the word "Shen" is pronounced qim, "Xin" is pronounced sim, "Jin" is pronounced gim, "Chai" is pronounced zim, and the vowel is "-im", which shows that it is because of the sound change in ancient and modern times.