Are there exceptions to using definite articles for body parts?

Question

In a test, I got the question "Yo _____ mis manos en el agua". The verb was sumergir. Is it more correct to say "mis manos" here than "las manos" and if so, why? Are there certain verbs you are more likely to or would always use the possessive rather than definite?

Answer

Hola David,
as a general rule we don't tend to use the possessive when the part of the body we are referring to is the subject's own body. So, generally, we would say "Sumergí las manos en el agua". If we used the possessive that'd mean that we somehow would like to emphasise that it was "my" hands. If it is not a reflexive verb, like in this case, you may find the possessive; however with reflexive verbs normally referring to hygiene it would be quite odd to use the possessive: "Me lavé mis manos." (¿¿¿???) "¿Te has cepillado tu pelo?" (???¿¿¿)  "Se torció su tobillo" (???¿¿¿)  However it wouldn't be that odd to say for example: "Metí mis pies en el agua" or "Puso sus manos en la mesa" 
Saludos
Inma