Hmmm I am limited to one post per day, so I will try to reply to all 😄
Many thanks to the all of the replies, especially TwiceBorn. No need to apologize, unless I say I read, no reason to assume I have. I mean, I did once, but it did not stick. I DID go back and re-read the skill entries for this, but that portion is much more detailed.
I keep forgetting how railroady CoC is. it is not a bad thing, but it is different. my foundational game is a mish-mash of dungeons and dragons and advanced dungeons and dragons, and so, from the start, very confrontational with the players. And you are expected to watch the players flail away, missing clues and such. Design advice for dungeons tells you to expect the players to miss as much two thirds of any level, for various reasons. I forget that this game is different. There is no treasure hoard, no levels, no resurrection. There is only the plot, really, the plot, and the mystery. I will have to adjust my thinking, consciously.
And yes, a failed spot check can be very useful, you can crank up the tension by only giving them partial info, enough to know that something is happening, but not enough to feel like they have it under control...
Thanks again, everyone. It is very nice to be able to ask for advice to improve my table skills.