Not to mention that Mandarin would use 嘴(里)rather than 口
The pronunciations of kanji correlate to different Chinese eras and areas.
The usage and choice of characters are influenced by Classical Chinese, which was the literary language in Japan until, uhm, recently-ish.
There is a very good recent YouTube video that explains the usage of Chinese characters in Japanese and which I recommend to anyone interested in the subject:
I've never learned Japanese,
nor spent much time there.
From my brother who studied Japanese for a while, the Kanji was a real blocker for him.
So I did wonder what it'd be like, given I already know a good amount of Chinese characters.
So in Mandarin you wouldn't find people using 食 as a verb, but in cantonese it is the correct verb.
In Cantonese it's pronounced something like "sekk"
("sihk" in Yale romanisation, but I think if you're not familiar with Yale you'd try and read that "sick" or "sikh")
Edit: "sikh"