Smile when you say that (6)
I believe the answer is:
cheese
'smile when you say that' is the definition.
('cheese' is said to produce a smile in photographs)
This is all the clue.
(Other definitions for cheese that I've seen before include "Roquefort, perhaps" , "Feta, for example" , "Gloucester or Edam, say" , "Solid food made from milk curd" , "Solid milk product" .)