That look on his face is more than enough to stir something within Jiang Cheng. He takes the phone and puts his own number in, using his actual name rather than his name that he uses in education. To the world, he's still Professor Jiang Wanyin. To Sizhui, he could be Jiang Cheng for the time being. He saves himself as Friday in Sizhui's phone, just to hide it better, before handing it back to Sizhui.