Self-Reproduction
A common buzz-phrase heard in the context of computer viruses is that they are self-reproducing. Ken Thompson presents a delightful discussion on software self-reproduction in Reflections on Trusting Trust. Thompson says that: "In college ... One of the favorites [programming exercises] was to write the shortest self-reproducing program [in FORTRAN]".
Now, if self-reproduction is looked upon as purely a programming exercise, the ease of writing such code would be related to the syntax of the programming language being used. Consider the following C one-liner (source) that prints itself (broken into multiple lines to fit):