He lifts one finger.

"One jar, please!"

He forks over a hundred and five rupees and the oil in exchange for the mushrooms.

"Pleasure doing business! The name's Maru. I'm usually travel the route between Hateno and Kakariko, so hit me up if you find anything else interesting!"

Then he's spreading out the mushrooms on the floor of his wagon, humming to himself.

"I'll remember that!" she promises.

Link is distracted trying to remember what he can use instead of oil of vitriol. Are they going into the building?

Zelda is proceeding directly toward the promised Beedle, yes.

The inside of the marquee appears to be some sort of inn, laid out with beds and privacy curtains. There's a board on the wall with a few posted bulletins, a few tables where folks are eating, and an inner reception booth connected to the one seen on the outside. A man with a huge backpack is seated by the pillar at the center, counting rupees. He and his bag are also in colors. Maybe it's a merchant thing, so people know to go to them?

The man twitches when they step past the threshold, sniffs, and looks up at them, alert.

...she tries a hesitant smile, and approaches.

They can get a better look at him as they approach. He's pale-skinned, readheaded, with a smattering of freckles. His eyes track them intently, but cautiously, and yet... hopefully? He hops to his feet once they're near, and like he can't stop the words from spilling out of his mouth—

"Youhavearuggedrhinobeetle—I mean, I love rugged rhino beetles! If you have one wouldyouconsidergivingittome."

"A rugged rhino beetle?" she says curiously. "I'm not very familiar with different kinds of beetles." She knows exactly what she is about to unleash, and yet, she cannot stop herself. "What distinguishes rugged rhino beetles from other kinds?"

"Oh, everything! Rugged rhino beetles are found in Central Hyrule and the Faron region and are adapted to the more wet and earthy environments, which means they are the best of all the rhino beetles at digging in mud, and the hardiest of them all to survive the harsh rains! They're very easy to identify: green with yellow wings. The bladed and energetic variants live more east and north of here. My very favorite is the energetic rhino beetle, because of how fast and long they can fly, but they're so hard to find—rugged ones are more common, maybe because they're better adapted to their environment and don't suffer as much from hunting—"

And he will go on and on and on until he's out of breath, and then finally remember what he's doing.

"But! I was saying! Can you give me your rugged rhino beetle? In exchange, I can give you, uh, uh..." He rubs his hands. "A high-grade tough elixir, straight from Akkala! Lasts you ten minutes!"

Link looks vaguely perturbed.

...she catches that look, and wishes she knew what it was about, but she's not sure how to ask.

"Well," she says, "I didn't actually know we were carrying a rugged rhino beetle, but—Link, does that seem like a good trade to you?" Particularly considering that if she gets her hands on that elixir she'll be able to pull it out of her pockets at will forever?

"...yes, uh. How did you know that?"

"—come to think of it, that is a good question."

"Well, ah, Beedle has a sense for these things!" He flaps his hands awkwardly. "Beedle loves beetles!"

He fishes a corked bottle of clear, dark purple liquid out of his pack.

"Now, about that rugged rhino beetle...?" he asks hopefully.

Link fishes an wooden tube wrapped in coarse paper out of a pocket. He looks at Zelda questioningly.

She considers the situation for a very brief moment, then nods firmly.

He hands it over.

And Beedle forks over his payment. He does not check that the tube contains the promised beetle. "Amazing!" he whispers, tucking away his winnings almost reverently.

He shakes his head, as if awakening from a daze. "Now, did you two want something? I sell all sorts of critters, odds and ends!"

"Oil of vitriol, or spirits of salt. Half-ounce bottles."

"Vials I have! So useful for storing insects, those." He opens a compartment on his pack next to him to reveal a line of small glass containers, each holding a little bug or two. "Acid, though... I don't usually stock that. But since you've done me such a big favor today"—he almost squees that last part—"maaaybe I can figure something out. How much can you make it worth to me?"

"Well, if we get what we need, we'll be making some elixirs, which we might be persuaded to sell to you if you're interested. And we're planning to travel quite a bit, and I'd be happy to keep an eye out for interesting beetles along the way."

"Oh, no! Beetles, Beedle's greatest weakness..."

He lapses into thought.

"If you promise to trade me the next... three rhino beetles you find... you can find me at any stable you go to. Then I'll give you some spirits of salt."

"It's a deal!"