Trixie tilted her head as she came upon the odd conversation, curious as to why he's talking to a rock. She can tell something magical is going on, even if she can't quite hear the conversation.

"Am I going to have to watch what I use in my transfigurations if some rocks are as sentient as you make this one appear?" Not having been able to hear both sides of the conversation, she couldn't tell if he'd actually been communicating with the rock, or just manipulating natural magics to make it seem that way.