The way it works:
You post saying what you want to do. (Say, creep up closer to hear better.)
In my post I then tell you what happened. (Nobody seems to notice, Hornet is on watch and notices, a giant appears and attacks, whatever.)
If you need more information in order to post always feel free to ask - either in a PM or in the Q&A section. Doing what you did - posting with and "Assuming this is possible" in parenthesis is also possible. Just be clear about what you want to do if, say, there are no good hiding spots available.
In this case - this is a rugged ridge line with a road going up it in switchbacks. The road itself and a few feet on either side are clear and easy to see. If a cat tried to cross the road they would be very likely to be seen. But once off the road the terrain is very rough - there are many verticle areas, trees, rocks, bushes and weeds. In general it is rough terrain for travel and easy to hide in. So . . . for a cat - you would fully expect to be able to hide and probably get within 10' of people given your size and natural cat-like stealthiness. You might be able to get within 3' if you wanted to risk it, but that would obviously carry much greater risk of discovery. Also, it depends on what actions others (PC or NPC) specifically take. If nobody mentions keeping an eye out, the odds of being seen are very low - it is essentially a passive perception check but you have many factors working to your advantage In this case it is worth noting that Hornet specifically said he was keeping an eye out for anything. So he is actively watching. Given the terrain and the cat you still are pretty likely to be able to move closer. But I would give Hornet a reasonable roll - that is what being on guard is all about.
And one last thing - In some cases it might be helpful to know the outcome of an action right away. Feel free to tell me (PM or Q&A post) "I want to do this - can I know the outcome before I post so that I can include it?" There will be times when the answer is no, but many times it will just speed things along to be able to do this. Just ask.
It was a good post - the sooner we get everyone popping up and decidng what to do with the snide little green-blooded goblins the quicker we can move on.