Adjective agreement

Question

I am curious as to the agreement of the adjective “délicieuses” in the dictation-surely it is the noun “l’air” rather than “moules” which it has to agree with? In other words, “the mussels look delicious”.

Accepted Answer

Katherine ‘ avoir l’air ‘ is an expression with interesting agreement rules. 
Agreement ‘délicieuses’ with ‘ moules ‘ is correct. (Basically here ‘avoir l’air’ is treated as a verb expression - “ les moules ont l’air (semblent) délicieuses “
According to Larousse - agreement with the subject when it is a ‘thing’, but agreement of the adjective can be either with ‘ l’air ‘ or with the subject for a person. ( Larousse doesn’t indicate any real change in meaning according to the agreement choice with people) . 
L'accord de l'adjectif attribut se fait avec le sujet quand il s'agit de nom de choses : Cette poire a l'air bonne ; avec le sujet ou avec air s'il s'agit de noms de personnes : Elle a l'air intelligent [e].
 https://www.larousse.fr/dictionnaires/francais/air/1940#locution  
The safest bet is to always agree the adjective with subject with ‘ avoir l’air ‘ !