Mystery Behavior

There is another office habit that Morey has picked up that has me puzzled. I currently have no working hypothesis and am still in the information gathering phase. Any input would be greatly appreciated!

Observed behavior: Whenever a co-worker comes into my office, Morey goes and gets a drink before going to greet them. A long drink, not just a few laps. After he has completed this behavior, which is now almost a ritual, he will go and eagerly say hello (usually timing his after- drink drool flinging until he gets close enough to "share" it with them). Lovely.

Facts:
Only does it with co-workers, people he is familiar with and likes, not with any other people who come in my office
Has access to water at all times of day

Possible motivation: ?
The people he does it with are my co-workers who love him and give him lots of attention. Possibly he feels overwhelmed when they say "hi" and goes to get a drink as a way to calm himself before greeting them?
-Seems unlikely, as my co-workers always interact with him very appropriately, not in a way that seems overwhelming (at least from my perspective)
He sleeps under my desk most of the day. Maybe when he gets up to say hello to them he remembers that he is thirsty and goes to meet that need before getting petted.
-I might be exaggerating Morey's laziness and his lack of motivation to meet his physical needs

Any other opinions/theories would be welcome. I'll post updates on this mystery once I have done more research and have more information to report!