"With"? (He walks away)
Robin: Okay, but you have to admit that he is a lot of fun. As in, a dog. Barney: There is an exception. Guys! It's a heart monitor. She seems like something special. Ted: I suppose it's possible Barney has real feelings for Nora. Wrong preposition.
Plan: A: Barney; Q: Who worries that he has a problem with his heart? A: real feelings; Q: What does Barney start to have for Nora? A: his heart; Q: What does Barney worry is wrong when he starts to have feelings for Nora? A: Robyn; Q: Who starts dating a guy who acts like a dog? A: a lot; Q: How much does the guy Robyn is dating act like a dog? Summary: When Barney starts to have real feelings for Nora, he worries that there is something wrong with his heart. Meanwhile, Robyn starts dating a guy who acts a lot like a dog.