A/N: For the March 5th prompt - "What are you waiting for?" Rated K. You can look up the Stanford Marshmallow Experiment on Wikipedia, it's fascinating. (I'm a one-marshmallow person, btw.)

"You, Sherlock, are a one-marshmallow person," John declared after looking up at Sherlock from his laptop. Both men were seated in their chairs, Sherlock glued to his mobile.

He finally looked up after a moment, confused. "What? I don't even like marshmallows."

Mary grinned at her husband from where she sat on the floor between the chairs, playing with Rosie. "I told you he wasn't human." She turned to Sherlock. "You're a changeling, right?"

Sherlock rolled his eyes. "Mycroft tried to convince me I was adopted when we were kids. It would have worked – I would've loved to not be biologically related to him – except that I have my father's face and my mother's eyes." He looked back at John. "What were you saying about marshmallows?"

"The Stanford Marshmallow Experiment. They offered a group of children one marshmallow right away or two marshmallows if they waited patiently for fifteen minutes. It's about instant versus delayed gratification. You're all about instant gratification – designer suits, 8,000-threadcount sheets, your worst enemy is boredom, I could go on."

"Please, don't," Sherlock muttered.

"Meanwhile, Molly is a two-marshmallow person – she's all about delayed gratification."

"And how exactly do you know that?" Sherlock asked, one eyebrow raised.

John smirked. "She's still waiting for you to get your head out of your-"

"Little ears, John," Mary said, smiling a bit.

"Right, sorry," John said, smiling apologetically. "Out of your bum."

"I told her that she's the one person that matters the most, isn't that enough?"

"That was a year ago so no, it's not," John pointed out. "You love her. I suggest you tell her before she gives up being a two-marshmallow person and finds someone else."

Molly opened her front door to see Sherlock standing there with a bouquet of yellow roses and a bag of marshmallows.

"Sherlock? What's going on?"

"You have a fireplace and we have something to discuss, Molly," Sherlock said, grinning. "Got any skewers?"