That exit confirmed his suspicions; there was someone else talking to Keenst while they were interacting. Sans mumbled to himself:<br/><b><br/>
* </b>sounds like someone 'was' talking to him, and was sparking him to attack. sounds too familiar...<br/><br/>He watched them leave the tavern from the backdoor and decided to follow, remaining hidden by teleporting into a crate to listen in. Something about him left Sans rattled. The situation was too familiar not to investigate further.