"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.
So Han føner håret sitt would be OK but the sitt is not needed in Norwegian (unlike the his in English)?