Is it just humans that get runny noses?
Are humans the only animals on Earth the only animals on Earth that secrete mucous from their noses?
No, we're not. Lots of creatures do have sticky noses and it's all about protecting yourself from those things you might be breathing in. Basically it's a layer of stickiness to catch dust and, more importantly, viruses that might invade your delicate mucous membranes. Things get breathed in and whirled around in your nose like in a miniature dyson vacuum cleaner, and then they get flung to the sides where you've got these sticky walls. Then you blow your nose and get rid of it, or swallow it so it gets broken down in your stomach.