Many studies have examined Instant Messaging server logs containing messages that were sent. Such studies cannot address questions about client activity during message composition because the necessary information is not available at the server. This study examines keystroke level data to understand what is happening between the sending of messages. Sixteen pairs of participants used Instant Messaging to solve a problem. Even though this task was designed to fully involve the participants' attention, only 43% of the time was spent actually typing messages. An average of 12% of that composition time was spent revising text that had already been written, often making substantial changes. These results demonstrate an opportunity for improvement of user interface features to better inform the user about the other person's activity in order to improve the efficiency of message composition.