[Light pauses. It would look suspicious if Sayu stopped talking. But did it matter in the end? If Sayu did stop talking to Mello, Mello could probably guess that Light had gotten in contact with Sayu.. which considering the previous Mello's behavior would provide little illumination on Light's character. One didn't necessarily need to be Kira in order to be concerned about their younger sister speaking to strangers. In fact, it would almost be stranger if Light hadn't been watching the feeds.

What does matter, is the fact that by interrupting this conversation, Mello would realize that Light is watching the feeds. The thought obviously hadn't occurred to the bastard yet, so why give him a hand? It's inevitable however, that sooner or later Mello would figure that much out. He's not worthy of standing in L's shadow, not in the slightest, but he's not an idiot either. ...At least, not a complete idiot.

Unless, Mello's true intention in all this, isn't to talk to Sayu, but to send a message to Light. I'm watching you. Or something along those lines. His eyes narrow at this thought. If there's one thing Light would not tolerate in this, it's involving Sayu.]

Relax. You haven't done anything wrong. [Yet.] Be careful. If he shows any sign of wanting to meet, refuse as politely as you can.