In this answer, I learned that with "correct" French, you aren't supposed to use possessive determiners for body parts ("ma tête, mes jambes"), but instead use a definite article ("la tête, les jambes"); but that in relaxed French, you might see possessive determiners used.
In this TV show (around 0:54), a superhero needs a kid's help on doing a physical exercise called "The Airplane", and is giving instructions to a kid:
Pour faire l'avion, je m'installe sur le dos, comme ceci. Je replie mes jambes et toi, tu vas appuyer tes hanches ici (points to belly button), sur mes pieds. Et tu vas mettre tes main dans mes mains, et nous allons décoller et redescendre. Ça te va?
I'm curious why he sometimes avoids using a possessive determiner with a body part, and sometimes doesn't. For example, he avoids it when he says: "je m'installe sur le dos", but uses it when he says "Je replie mes jambes" (instead of "Je me replie les jambes").
Here is a bonus example that might be useful to have explained to me: in this show for children (at about 1:35), a woman sings to the audience about her love of fixing things and making crafts:
Avec mes deux mains mains mains,
Avec mes dix doigts coquins,
Je fabrique brique brique
Je bricole colle colle
Des idées plein la caboche
Fabricoler c'est fastoche.
I'm wondering if she could have said "Avec les deux mains" and "Avec les dix doigts" instead, and if it would have the same meaning / connotation, or if there instead would have been a difference?