Spanish language Q&A Forum

How would you write “My leg and knee hurt”? It seems like I could write it “Me duele la pierna y la rodilla”, but not “Me duelen la pierna y la rodilla." Are either of those correct?

I have encountered real-life examples using both indicative and subjunctive with "una vez que..." and I'm just hoping to confirm or correct my understanding of how this works, please...? For examples, In an article about animals' senses of smell, in discussing the properties of volatile scent compounds I read "Una vez que se vaporiza, puede extenderse rápidamente por el aire" and in a tutorial for making tortillas mexicanas I found "Una vez que sepas cómo hacer tortillas..." I'm thinking that the first takes the indicative because its describing something factual understood to happen routinely, whereas the second takes the subjunctive because it's referring to something that from the writer's point of view hasn't happened yet or is more a hypothetical idea. Is this an accurate way to understand this or am I missing something...? If this is accurate, does it generally hold true with other, similar constructions like those discussed in this lesson? Thanks in advance, as I appreciate the help!

I was taught podrías means could when talking about the future and podía means could when talking about the past. Is this wrong?