I guess I'm not getting the "common sense" part because I absolutely believe that PF could have done this on his own and didn't need KK there swinging the bat for him. The candle sniffing may have just presented an opportunity for him.
Scenario:
PF and KB are inside her condo. She's just bought a couple of new candles. "Here," she says, holing it out to him, "this is meant to be Apple Cinnamon but I swear it smells like vanilla."
He takes a sniff. "Smells like apple to me," he shrugs.
She picks up another one marked "vanilla." "No, see? Smell this one and then smell that one? They're exactly the same!"
"I don't see it," he laughs. "They smell the same to me."
"I paid $20 for this Yankee," she complains. "I already had a vanilla one..."
"They're all the same," PF tells her.
"No they're not! They all have a distinct aroma. Why do you think we women collect so many?"
And then, upon looking around her living room, he gets an idea. "If your nose is so good then do you think you can tell what all these candles are without looking at them? I'll bet you $5 you can't."
"Ha, try me."
The baseball bat she uses for defense is in the corner of the room. He'd meant to so something to her the night before, he'd chickened out. Now he's feeling a burst of adrenaline. It all clicks into place. PF goes around, collects half a dozen candles, and lines them up in front of her. "And you can't cheat, either," he says as he wraps the sweater around her eyes.
IMO PF is a few fries short of a Happy Meal, but I think he was perfectly capable of killing KB all by himself.