For the example you give, in Cantonese they're dou6 and dok6, respectively. The 3/6 tones in Cantonese and ˋ (4th, falling tone) in Mandarin are the "departing

For the example you give, in Cantonese they're dou6 and dok6, respectively. The 3/6 tones in Cantonese and ˋ (4th, falling tone) in Mandarin are the "departing" tone, which comes from the departing tone in Middle Chinese, which I believe comes from the -s ending in Old Chinese.