It may well depend on your tact and your relationship with your intern or resident. I have never had a problem stating something that I think is correct or sharing my opinion, even if it's contrary to what someone more senior has stated. I rarely interject, but if I do, I make sure it's necessary and correct, before I speak up, and I will do it diplomatically. Usually, I state it as a question rather than as a statement. For example, if we are looking at a diabetic with a high serum glucose and evaluating for hyponatremia, I might say something like this, if I think it's being overlooked: "When we are evaluating this patient's serum sodium, should we correct it based on his glucose?" Something like that usually garners a response like, "Oh, yeah, that's a good idea; here's how we do it," or, "Good idea! How do you think we should do that?" Sometimes, my question will get ignored, but I'm usually glad I said something, because I'm usually pretty careful about it.
FWIW, take time to make your intern or resident look good when you can. It will pay off in spades. Trust me.