Airplanes and Z

We were playing on post last night at one of the parks and an airplane was flying overhead. Z stopped playing and looked for it (like he usually does) and said "Is Mark on that airplane?" I told him no and that he would be home soon and he went back to playing. We have seen hundreds of planes and this is the first time he's mentioned Mark when seeing one! Not sure if it was because we were on post ("Mark's work" as we refer to it) or if he was just thinking about him. Mark is obviously on all of our minds!