Tu cabeza v la cabeza

Question

In the example La pájaro vuela sobre tu cabeza, why is it "tu" cabeza. I thought when talking about body parts and clothing we should use the definite articles rather than the possessive adjectives.

Accepted Answer

Hola Fiona
We generally omit the possessive and use the definite article when it is absolutely clear that we are referring to the subject's body part, for example:

Se puso crema en la mano.
He put cream on his hand.

This is obvious because it's using the reflexive verb "ponerse" so we know it is his own hand.

Movió la cabeza hacia un lado.
He moved/turned his head to one side.

It's be unnecessary here to say "su cabeza" because you turn your own head.

Metió el pie en un charco.
He put his foot in a puddle.

Here it's also obvious.
In the sentence about the bird you need to specify over whose head it is flying, otherwise it wouldn't be clear. therefore:

El pájaro vuela sobre tu cabeza.
The bird is flying over your head.

I hope this clarified it.
Saludos
Inma

Answer

I think that it's because unless you use the possessive adjective tu, it would be unclear whose head the bird is flying over. It could be mine, yours, the person over there etc.