Easy question
do u say "she was eating a seaweed"
or "she was eating seaweeds"

Among the two options,"she was eating a Seaweed" and "she was eating SEAWEEDS", the last option and that is "she was eating SEAWEEDS" is the correct answer. When you are saying "she was eating a SEAWEED" you mean to say that she was eating a single seaweed and that is next to impossible. In the second option, when you are saying that "she was eating SEAWEEDS", it did not specify any number of seaweeds and so it is quiet possible that she was have a good amount of seaweeds to satisfy her hunger.

Neither. Its She Was Eating Seaweed. :)