Leonard stared blankly at the sheet music that was set before him, completely lacking his normal enthusiasm. Without even paying attention to what he was doing, he followed the boring cycle that had been going on for the last twenty measures.

D, A, B, F#, G, D, G, A.

With every note, he slowly felt his interest in the cello draining from him. It was absolutely the most lackluster performance he'd ever done, and he felt Leslie kick him, giving him a condescending look.

The lucky violinist. She had a fun part, the part that made orchestra teachers who were primarily violinists force their cellists to play this wretched song.

The cycle started over.

D, A, B, F#, G, D, G, A.

Canon in D would never end.

Staring glumly at his food, Leonard ignored Sheldon's babble about the importance—or, rather, lack of importance—of sporks, sinking into the recesses of his mind.

After finishing the practice for Leslie's cousin's wedding, she had chewed him out about how distracted he was during the practice. Threatening him with all sorts of horrible punishments if he did the same thing at the actual wedding, she had left Leonard discouraged and in a really bad mood.

Apparently nobody was noticing; Sheldon was now talking about how to survive a zombie apocalypse, Raj was arguing with him, and Howard was on his phone, texting Bernadette. Biting his lip, he decided he couldn't take it any longer. Without a word, he stood to his feet, and decided to go visit Penny.

As it turns out, Penny was at home, and actually in a good, friendly mood. "Hey!" she chirped in her naturally cheerful voice. "How are you?"

Immediately, Leonard launched into his story of his woes. "It's just awful, Penny!" he announced, walking into her apartment without an invitation. "Leslie said I owe her a debt for borrowing the lab from her one time, and so she's forcing me to play cello for her cousin's wedding. And it's Canon in D."

He expected for her to be confused, for her to ask, "What's that?" Instead, she said, "Oh lord, I feel your pain?"

Looking at her, with one eyebrow raised, he asked, "Really? You do?"

Shrugging, she nodded. "Yeah. I've heard Pachelbel Rant; it sounds just awful to play."

For not the first time in his life, Leonard had no idea what Penny was talking about. "Wh-what?"

"Pachelbel Rant? Oh my god." She started cracking up as she continued to get a blank look from him. "Leonard, you'll love this. Hold up. Sit on the couch and get comfy; I've gotta show it to you."

Ten minutes later, Leonard had been settled, and had watched the video… twice. Still, even after the second time, he was cracking up, tears spilling down his face from sheer, accurate humor of the act. "Th-that was the best thing ever!" he announced to Penny, who just nodded in agreement with a smile on her face.

Now he could face this horrific piece.

"How'd the wedding go?" Penny asked as she folded her shorts, not even bothering to look up at Leonard.

"How'd you know it's me?" he asked, carrying the basket in.

"Not Saturday," she said, making him say, "Ahhh," as he set his basket on top of the dryer. "You've gotta tell me how it went," she said, not letting him change the subject.

"Uhhh…" he said, looking down at his face. Refusing to look her in the eye, he said, "Leslie… uhh… she's not very happy with me."

"Uh oh," Penny said, rolling her eyes mischievously at him. "What'd you do?"

"Well… We were about halfway through Canon in D, and… well… my head suddenly started chanting, 'Pachelbel, Pachelbe-e-el, I'll see your ass in hell,' And I, uhh, started cracking up in the middle of our song."

Instead of sympathy, Leonard was met by laughter from Penny. And he was laughing too, without even realizing it.

That's the power of the Pachelbel Rant; it makes people laugh randomly.