"Hey!" Liam protested. "I can hear you two thinking at each other."

Not entirely true; Sarah's telepathic presence was the same as usual, like listening to a familiar piece of music being played in an unfamiliar key, but he wasn't a telepath, he couldn't hear anything she didn't choose to project directly at him. And Renee certainly wasn't a telepath (at least, insofar as they could tell. There'd been that weird incident with Jeff, but all the evidence pointed to him being the telepathic one). So yeah, Liam had no idea if that was actually what was going on, but it seemed like a reasonable guess.