I consider myself a pretty advanced English teacher and user. Nonetheless, I've recently found myself in a pretty difficult spot trying to explain which of the following sentences is correct:
My favourite animal is a dog
My favourite animal is the dog
My favourite animal is dog
My instinct tells me the dog is the correct one, but I've found so many instances on the internet where native speakers say My favourite animal is dog that makes me wonder if that sentence is also correct.
Additionally, I know that a sentence like My favourite food is pizza sounds pretty right to me, making the whole thing so complicated that I cannot figure out any rule that governs using articles in the above sentences.