I don't understand why "it" is used when what's burning is "my eyes" which are plural. Shouldn't it be "they"?

Native speaker’s answer
Rebecca
Good question! "They burn" would work just as well here as "it burns!" However, here, the "it" actually refers to what's in his eyes rather than his eyes. So, they're referring to the cause of the burning sensation. Ex: My feet are so cold. It burns! Ex: The hot water burns. Be careful.