"He blow-dries his hair."
Translation:Han føner håret.
It would imply that the subject(=he) is blowing someone elses hair. Technically it is not wrong, as the English sentence is ambiguous, but it would not mean the same: Han føner håret (sitt).He blow-dries his (own) hair. Han føner hans hår/håret hans. He blow-dries his (someone else's) hair.
Question because Norwegian and German sometimes have similar constructions and idioms: Could you use "føne" as a reflexive verb, ie say "Han føner seg"? Would that be weird, or would people think that he's blow-drying his entire body, or would it be understood that he's just drying his hair?