B o n d
Have you noticed that Quatre somehow talks to Sandrock? Well, Quatre thinks of Sandrock as a real being. So that's why he talks to it. I mean all gundam pilots have a bond with their gundams, even the quiet ones like Heero and Trowa. Quatre thinks of Sandrock more of a partner in battle than a machine he's sitting in. When it's time to fight, he'll say, "Let's go Sandrock!" Some people may think this is crazy but I think it strengthens the gundam. This just goes to show you how sad he might really be inside when he lost Sandrock. Anyone will get attached to something or someone that's been with you for a very long time right?
In EP 17 when Quatre activated his self-detonation device and was prepared to die with it, Sandrock automatically opened its cockpit entrance as if to let Quatre escape. It even walked away so it wouldn't destroy Quatre in its explosion.
An attempt at the actual dialogue
Quatre: Are you telling me to get off?
Quatre: Thank you Sandrock!
(it starts to walk on its own as Quatre got off)
Quatre: Thank you, my dear Sandrock.
We are assuming that Instructor H installed this program in Sandrock whenever the detnation device is activated. It isn't confirmed though. Could Sandrock possibly have a mind of its own? We never know. ^_^