Derpy looks ashamed that she suggested it, but the offer is certainly tempting. Her hooves are probably still tired from all that walking she'd done today, why you'd be rude to deny her the mouth-massage she deserves. You give her a seductive little glance that speaks volumes. Derpy looks away, bashful, but she knows what you want. She plops herself down on her haunches and extends one of her hind hooves to you.
"Thank you," She says in advance, "And sorry, they're kinda stenchy."
You take a sniff and find wasn't lying. Her underhoof smells sort of cheesy and salty, like cheddar popcorn. The aroma makes your mouth water And you nuzzle your nose against it to get a better whiff. Some of the dirt she'd accrued while trotting along Ponyville rubbed off on your nose.
"I like it," You say, "It's a nice, strong scent."
"Wow, you really like it?" She raises her other hoof to your nose, doubling the smell, "Like this one too?"
You can only moan as the aroma of her sweaty, overworked hooves invades your nose. It's incredible, you're always amazed at how badly a hoof can stink. Yours can get a little smelly sometimes, but nothing rivals the scent of another mare's hoof when it comes to turning you on. You stick your tongue out just to taste it. You get a bit of the gritty dirt in your mouth and swallow it up.
"You're so tasty Derpy,"
She blushes, "Don't say stuff like that, it's... weird."
You lick her hoof again, trying to get every last sweaty morsel of dirt from it. You lick from every angle and coat her underhoof in spit. You're actually surprised your mouth didn't get dry. It must have been all the salivating you were doing while sniffing her. Eventually all that flavor is gone and you have to switch over to the next hoof, which is still ripe with her smell.
"Screw it." You think to yourself. You were contemplating just taking your time with this one, as you had with the first, but you just can't wait. You open your mouth as wide as you can and manage to stuff the entire sole inside. You slurp and suck, pulling every last drop of dirt and grime off her hoof. You find your own hoof drifting down to your crotch. Derpy places her free hoof over your nose so you can fully enjoy the scent that so strongly clings to it.
"Oh Muffin," Derpy moans, "Muffin, you're so great..."
You can't even hear her anymore; you're far too busy clopping to the scent of her filthy hooves. The texture, the taste, the smell, it's too much. You cry out, muffled against her hoof, and come. Derpy notices almost immediately and pulls her hoof from your mouth.
She giggles, "You sure do like hooves, don'tcha?"
You nod and smile. It's a goofy smile, one that's still a little high on afterglow.
"Yeah, I-"
You both freeze up. Someone's close. You could hear someone nearby and you feel like you were caught with a dead body. You can only imagine what Derpy must be going through. The shrub you were hiding behind rustles and you can see, in the darkness... It's...