From The Art and Popular Culture Encyclopedia
Amusement is the state of experiencing humorous and usually entertaining events or situations, and is associated with enjoyment, happiness, laughter and pleasure. Amusement may also be experienced through the recollection of events which have given rise to amusement in the past.
Humans will typically laugh or smile to display amusement. For most people at some time, situations which would normally elicit amusement may not always have the same effect, due to various reasons such as one's state of mind. People with certain disorders or disabilities may sometimes appear to experience amusement without an obvious cause or reason.
Although various animals may be perceived as experiencing amusement, this may simply be a case of anthropomorphism. Interpretations of "amusement" may be attributed to animals that do not behave as expected, such as where an animal runs instead of walks, or becomes more alert. Other animals such as dogs may wag their tails or spin around, birds may chirp more loudly or frequently, while racoons or bears may not react at all.
However, there are instances of animals reportedly, "playing jokes" on other animals or humans. While they may not show any outward signs of amusement, it would seem as if there is no other explanation.