Smeagol didn't know what Dobby was talking about, but decided to go along with it. Dobby said he was here to help? Okay.
"Pardon me, Dobby, buy I'm looking for the Precious. Have you seen it?"
Dobby was intrigued by the hideous, fish-scented, loincloth-wearing guy the Room of Requirement had produced for him. "Dobby does not know what the Precious is, though Dobby would be happy to help!"
"Well, the Precious is a ring, small, solid gold, and definitely belongs to me, Smeagol. It was given to me for my birthday and I've lost it. I'm afraid the whole situation is rather embarassing. Can you help me to find the Precious?"
Dobby thought that naming a ring was pretty dumb, but pretty much everything wizards did was dumb. Ever since his race had allowed themselves to be shackled into servitude by the apes to alleviate their eternal boredom, he had been beseiged be one stupid order after another. Whatever. Fucking with this diminutive deformed wizard while pretending find a ring sounded like excellent practice. He'd asked the Room of Requirement for a chance to test his cunning, and here it was. "Would Mr Smeagol say that finding the precious is... nothing less than his heart's deepest desire?"
Smeagol nodded.
Dobby laughed. "Perhaps, then, it is in Dobby's cloaca! All sorts of wondrous things find their way there. Here, take a look!" With that, Dobby doffed his pillowcase and bent over.
Smeagol was suspicious. This was incredibly stupid. However, he weighed the cost of peering into Dobby's cloaca against the potential benefit of actually finding the Precious. Even accounting for the heinous improbability of finding the Precious, it was a minor inconvenience and he had a crippling emotional dependency on the Precious.
"Okay, Dobby, dilate your cloaca and let me have a look. I hope this is not a trick."
Dobby, his grin hidden by his ass, torso, and the majority of his head, complied. He had a trick up his sleeve - or rather, his cloaca. Last year when Dumbledore needed to hide the Mirror of Erised, he'd realised the Lucius Malfoy's House Elf's cloaca was the last place anyone would look, and placed an Undetectable Extension Charm on Dobby's cloaca in order to hid the Mirror.
Smeagol peered deep into the dilated flesh-hallway. It went much deeper than he would have thought possible. But there! In the deep darkness, he saw it. He saw the Precious!
"I see the Precious!" said Smeagol. He thought he did, but he didn't really. It was the Mirror of Erised tricking him. But he was a greedy shit and shoved his calloused, cave-worn hand right up Dobby's cloaca. The hole clamped down before his wrist even cleared Dobby's sphincter and stuck there.
"Mr Smeagol!" said Dobby, "Dobby admonishes you!"
"Please give me the Precious, I would like it very much!" said Smeagol.
"Dobby thinks it might be further than Mr Smeagol can reach, but Dobby is willing to let Mr Smeagol try. But Mr Smeagol must promise not to be rough!"
"Of course," said Smeagol. "I do apologize for that earlier rudeness. Now, if you could unstick my hand, it's currently both ensconced in your cloaca and not wrapped around the Precious. I'd like to remedy one, if not both, of those problems."
Dobby re-dilated his cloaca, allowing the foolish, ugly wizard to extend his bony arm further and further into his cloaca dimension. He laughed to himself a bit in his obnoxious House Elf titter. Mr Smeagol would never be able to reach the Mirror and call his bluff.
Smeagol was shoulder-deep in Dobby (which was impossible, he reflected, but he was reaching for a ring that turned him invisible, so: fair). He reached and grasped and flailed his arm, the House Elf gleefully waving around in the air. A gentle peristalsis gripped Smeagol's arm and began pulling it in further, forcing it up against the knob-like calcified protrusions lining the entrance to Dobby's cloaca. Smeagol became angry and began choking Dobby with his other hand, the one not embedded in Dobby's only lower orifice, but it just seemed to excite the elf further.