Performance study of new employees

So for the first time ever, I trained someone for their first TWO shifts (rarely does that happen because you always want new employees to work with different people to pick up different things etc).  What I discovered baffled me.  This new guy, lets call him Bob (his name is definitely not Bob) worked A LOT harder on his first day.  The desire to make a first impression was hard at work there! Yesterday he showed more of his true nature. While still working harder than most people there (hmmmm perhaps he just realized he didn't have to do much to be better than most other employees) he definitely sharply dropped off from the previous day.  To the point where he didn't even bother to study our menu. Should be fun to see how the rest of his training pans out. Still have high hopes for this "Bob"