Questions & Answers about Son cou est long et mince.
Why is it son cou if the translation says "Her neck"? Shouldn't it be sa?
In French, possessive adjectives like son and sa agree with the gender of the noun that is owned, not the person who owns it. Since cou (neck) is masculine, you must use son, even though the neck belongs to a woman. English speakers often trip up on this well into the intermediate stages!
I was taught to use avoir and "le/la" for body parts (e.g., Elle a le cou long). Why does this sentence use son and être?
You're absolutely right that Elle a le cou long (literally "She has the long neck") is the most common and idiomatic way to describe someone's features in everyday French. However, using a possessive adjective and être (Son cou est long) is also grammatically correct. It tends to sound slightly more literary or descriptive, placing the grammatical focus entirely on the body part rather than the person.
Since long is masculine to match cou, what would the feminine form be?
The feminine form is longue. If you were describing a feminine body part, such as a leg (jambe), you would say Sa jambe est longue.
Does mince only describe people and body parts, or can I use it for objects too?