There is a scene where Alan and Charlie drink, at the sound of a bell. They're doing this in a bar called Pavlov's. Russian physiologist Ivan Pavlov used classical conditioning to train a dog to respond to a certain stimulus, where they get a reward for that response. Just as Alan and Charlie responded to the bell, by drinking a shot.
Conchata Ferrell saw the role of Berta as a way to reflect her past as a hippie and political activist in the 1960's. While the role didn't call for any real political or social elements, Ferrell felt that Berta would treat Charlie Harper (and later Walden Schmidt) like a modern version of "The Man" and get away with it because she wasn't afraid of being fired by either of them.