Why is Entlebucher called the laughing dog?

Why is Entlebucher called the laughing dog?
The Entlebucher Mountain Dog is called the “laughing dog” because of their lively, expressive eyes and spirits as high as the Alps. This nickname highlights the Entles’ cheerful personality and the way they seem to “smile” when they are happy or playful — which, with their joyful spirit, is much of the time.