It’s a feather. Not one from a bird you recognize… but somehow it’s familiar.
And then you remember. You reach into your pouch and pull out an identical one. It’s supposed to protect you from long falls… though who knows if the magic even works with all you’ve been through.
You also have no way of knowing if this feather is also enchanted. But the match is so close that you’re certain it’s from the same type of bird – probably one from the desert.
So maybe this is someone from the desert. Maybe even from the same place as Ember, not that you know where that is. And a funny thought’s crossed your mind.
What if Ember’s people want the staff? What if there’s some kind of deal between them and the Marshguards over it, and that’s why the person here was acting so weird – they thought you were their contact. And now a lizard they were keeping in their bed is near the staff…
…and marked your shoes with its spit. Potentially identifying you somehow to its master.
You’re making a lot of guesses right now, and you’re not sure any of them help you even if they’re right. You think your best move is figuring out where the patient is, whoever they are. Because you do feel pretty confident in your guess that they’re the eavesdropper.
In which case, wouldn’t they have heard you already and gone into hiding? So you’re basically trying to guess where they’d hide.
Suggestions:
If your theory is correct, you’d better keep your eye out for someone from the swamp.
Check under the bed.