Hello,

I noticed that oler seems to be sometimes built with the preposition "a" before introducing the smell of something, such as in:

Tú hueles a perfume fresco. 

or

Las galletas huelen a chocolate.

So I thought it was used in the meaning of "smelling like something", when the subject themselves smells like something. But then I also noticed it in ¿Vosotros oléis a pollo quemado?".

So is the "a" used rather when the smell has no article? What is the rule (if any)?

Thank you!