To take a statement with 'a grain of salt' or 'a pinch of salt' means to accept it but to maintain a degree of skepticism about its truth. --The Phrase Finder
We use idioms with little thought. We know what they mean, even if the saying itself bears no relation to the meaning. Well, except for when that's not true, when we have no idea, when we can't catch the underlying meaning and focus instead on the surface meaning of the words, you know, like my kids do.
This morning, my son (who is autistic and intellectually disabled) sat watching the news with me, and he started to get carried away with a story we were watching. I told him he needed to take it with a grain of salt. Immediately, I pictured him sitting there with a grain of salt in his hand as he listened to the news, so I quickly said, "I mean with skepticism." Okay, sure, I had to explain that to him, too, as his recall can be sketchy, but it makes it a great deal easier to explain as you don't have to go into the detailed discussion of colloquialisms, idioms, and cliches and why people say things that make no sense. There are some conversations best left until after the coffee has cleared the cobwebs.
After all people should be precise! So you start the wild goose chase of googling to find the exact meaning, and you and your literal child who has slowly been making you, too, hopelessly literal (to great fun, of course), and then there ensues a lively discussion about why people are using silly phrases that they themselves have no idea of the origin of or actual meaning of; after all, they're just going on a gut sense of what a phrase means (no wonder words are abused so!).
Yes ,and then that leads to a discussion of why people aren't curious about the etymology of the words they use, why they use them without care, without curiosity, without precision, and you're off again on a twisting whirl of a ride wondering why you didn't remember to handle your conversations with the boy with kid gloves, because after all, a leopard can't change its spots!
It would be silly, though, to find such discourse an albatross round one's neck, but I know that, at times, our children's lack of understanding is frustrating--we're impatient at times--after all, we know what we meant--it's easy as pie for us. Why isn't it for them?
Ah...and then, if we've any sense at all, we might realize we have another think coming if we believe understanding all these nonsensical phrases is an intuitive, easy process.