They're unable to hear or see the cars outside (5,4)
I believe the answer is:
cloth ears
'they're unable to hear' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'see the cars outside' is the wordplay.
'see' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'outside' is an insertion indicator.
'lo'+'the'='lothe'
'lothe' inserted into 'cars' is 'CLOTH-EARS'.
'or' is the link.
Can you help me to learn more?
(Other definitions for cloth ears that I've seen before include "One not attending" , "Person not hearing through inattention" .)