So what kind of action do they have to declare? Let's say my PC is in the woods. For whatever reason, they get an odd feeling*. They state they look around. You ask for a perception check - do they only see things? Could they also hear things? Smell things?
For that matter, what could trigger a perception check?
*This has happened to me when hiking. For example, I ... umm ... PC noticed fresh bear scat that's still steaming in the cool morning air. So they want to be sure there's no bear nearby.
This is extremely difficult for me to answer, since I didn’t create the scenario, and it sounds like you yourself don’t have all the specifics either. I’ll
try to engage with the question as best I can, but it’s… very strange.
So, if the PC noticed fresh bear scat, that must mean I described said fresh bear scat in my description of the environment. That would presumably be because I was telegraphing the presence of bears? I suppose it
could have just been set-dressing, but that doesn’t seem like the kind of thing I would just throw in for no reason. So, I’ll assume there are in fact bears somewhere nearby and the scat was meant to telegraph that fact. So, the player says they look around. Am I correct in assuming that their goal is to find out that there are bears nearby? If so, ok, we’ve got a goal (to find out if there are bears nearby) and an approach (to look around). I would then have to determine if that approach could accomplish that goal, if it could fail to do so, and if both are possible, how difficult it would be.
So, if there are bears, I imagine one could certainly find them by looking around. It’s not like they would be
hiding, they aren’t ambush predators or anything. Could looking around fail to find them? Sure, the woods are a pretty big place with lots of places you might conceivably overlook. Is there a meaningful consequence to failing to find them? I suppose so; if you don’t know they’re there you might be surprised if you run into them and they attack. So, I’d say this would require an ability check, using wisdom since attunement to the world around you, perceptiveness, and intuition are the most relevant factors in success here. I could see perception, investigation, nature, or survival being applicable. And as established, it would probably be an easy check since the bears aren’t likely taking any special effort to hide themselves. So I’d call for a DC 10 Wisdom check, and the player could add their proficiency bonus if they have any of the aforementioned proficiencies.