To lessen their angst after a whole day of acting out intense emotional scenes, Steven purposely snuck in some levity during his rehearsal with his on screen elder stepmother, Wu Qian Qian.
paraphrasing their words in interview:
WQQ, brokenhearted at her treatment at home, decides to leave the family she has served and loved for so long and Steven runs after her to persuade her not to do so. Steven pleaded with her his scripted line at the start but finished it with his own improvisation: "But before you go you should at least give me your QQ number ba?. " (similar to msn online chat)
Without missing beat, WQQ tearfully said: "I left it under your pillow."
source: pptv link