One of the many peculiarities that guide the linguistic facts concerns the inflections of the nouns, gender (male and female), number (singular and plural) or even degree (augmentative and diminutive). In order to solve them, a good suggestion is to read regularly, as well as the constant practice of writing and, to complete, some tips, which are always welcome, no doubt.
In this sense, the article in question aims to address one more question that prevails daily: the inflection of nouns relative to body parts. Now, in the case of two people or more people, whose idea is revealed by a compound noun, the normal thing is to establish the inflection of some terms that make up the discourse, although this is not always presented as a plausible reality, applicable. Let's see why through some examples:
"The brains" of humans are studied by scientists.
At the meeting, everyone lowered "the heads”.
Okay, it becomes explicit that it is more than one person, however each of them has only one head, only one brain and so on. In this way, know that the noun should not be inflected, which is why the examples above lack reformulation, which is manifested by:
The brain of humans is studied by scientists.
At the meeting, everyone lowered the head.
However, when it comes to some parts manifested by pairs, such as, for example, hands, feet, eyes, fingers, it is normal for such nouns to appear inflected, as well as:
At the meeting everyone stood up the hands.
they raised the eyes when the girls passed.
lowered the fingers after the teacher answers the questions.
When the intention is to refer to only one of the hands, it is natural that this noun is demarcated in the singular, as in the following example:
During the lecture, a question was asked and some raised the hand to answer.
By Vânia Duarte
Graduated in Letters
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/flexao-dos-substantivos-referentes-partes-corpo.htm