Why didn't Chewbacca talk to obi wan while on board the falcon heading to alderan?

We didn't hear the first meeting of Chewbacca and Obi Wan in the Cantina. They could have done a quick reminisce and then Obi Wan asked Chewbacca not talk about it in front of Luke. Luke didn't seem to be listening and was then distracted by the attacker.