This story occurs during the Season 3 finale of Person Of Interest, between the time Root and Shaw finish installing the 7 Samaritan servers and the next morning. Much of the Root/Shaw relationship was off screen, and I feel like this was one of those occasions when something happened that we never got to actually see.

What happened to Shaw after the show was cancelled

Shaw had never particularly felt that she was warmer than usual. Maybe it went with the anger and the constant action with missions. But it never bothered her. That is, until she met Root.

The one in which Root keeps writing coded messages to Shaw just to piss her off and Shaw wants to punch her in the face (as usual).