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 cannot judge whether this works.
'see the cars outside' is the wordplay.
'see' becomes 'lo' (archaic exclamation meaning 'look!').
'outside' means one lot of letters goes inside another (some letters go outside others).
'lo'+'the'='lothe'
'lothe' placed inside '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" .)