I watched a YouTube video about the difference between hypothesis and a theory. The presenter said,"we did a science!"

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Why did he use an indefinite article? How can the noun science be countable?

JigneshbharatiWhy did he use an indefinite article?

He did it to try to sound hip and trendy. He failed.

JigneshbharatiHow can the noun science be countable?

It can't in this context. Of course, it can be countable when used as in "Nuclear physics is quite an arcane science to the layman" or "The science of ecology has come into its own in the twenty-first century."