Cereal is singular, not plural. "We were eating cereal". In this case "the new episode" is correct, assuming that it is the latest episode availble for viewing. If you were catching up on a series that was released sometime ago, you would say 'a new episode', as it is new to you, even though others may already have seen it.

I agree with Hilary. One more thing about cereal vs. cereals. It would be correct to say cereals if you and the other person/people were eating different kinds of cereals (e.g. you are eating Frosted Flakes and the other person is eating Cheerios). This is not very natural to say though. We might hear 'cereals' in a sentence like: What do you want for breakfast? I have some different cereals, like Weetabix and Corn flakes, if you want cereal.

Hello Anita!!

North Americans tend to associate the word "cereal" with a common breakfast food (like Cheerios or Frosted Flakes). And like bread or cake, cereal is uncountable and therefore always singular. Theoretically, if you had a bowl full of a variety of cereal grains (ie rice, wheat, barley, oats...), you could say "We were eating cereals..." However, assuming you are not a horse, the first definition is more suitable.

“We were eating cereal and watching the new episode of our favorite series.” 🌈 Nicky 🤗