The recent spate of new, flashy top-level Internet domains (TLDs) includes one for the equestrian industry, .horse. Someone has used this and other TLDs to construct the following series of linked domain names, which you can view by tracing the route to bad.horse, either in Network Utility, or by the Terminal command
traceroute bad.horse

The output will start with a series of nodes which will take you from your ISP’s servers to bad.horse, and the poem will then read:

bad.horse
bad.horse
bad.horse
bad.horse
he.rides.across.the.nation
the.thoroughbred.of.sin
he.got.the.application
that.you.just.sent.in
it.needs.evaluation
so.let.the.games.begin
a.heinous.crime
a.show.of.force
a.murder.would.be.nice.of.course
bad.horse
bad.horse
bad.horse
he-s.bad
the.evil.league.of.evil
is.watching.so.beware
the.grade.that.you.receive
will.be.your.last.we.swear
so.make.the.bad.horse.gleeful
or.he-ll.make.you.his.mare
o_o
you-re.saddled.up
there-s.no.recourse
it-s.hi-ho.silver
signed.bad.horse

If you prefer to watch and listen to this, point your browser here. A fuller account of Dr. Horrible’s Sing-Along Blog is on Wikipedia; it was written by Joss Whedon, his brothers, and others as a three act musical.

Thanks to @mikeforbes via @Dave_Maynor for this profound and wonderful discovery.