SPROCKET: It's half full, because during the process of filling the glass, you stopped. You half-filled it.

HALO: It's both. It couldn't be half full without being half empty. One couldn't exist without the other.

One of the best stories is the aforementioned "Telemarketer", in which the title character tries his sales pitch on Halo and Sprocket over the phone. In a clever twist, Callen keeps Halo and Sprocket off-screen until the last panel. By telling it from the Telemarketer's point of view, Callen relies on our understanding of the characters to appreciate the humour. (This is really evident when you try to image somebody unfamiliar with Halo and Sprocket reading this particular story first.)

Another notable story is All's Well", which is only one page long. Halo and Sprocket travel back in time to avert disaster...by moving a vase "exactly two inches to the north". The absurdity of it all is made complete by the fact that Sprocket is inexplicably wearing a crown and carrying a tennis racket. (In his notes at the back, Callen states that time travel stories in which "nothing happens" should always be short. This is such a concise criticism of how often we're cheated by movies and TV shows in which, after a time travelling adventure, both the characters and the audience are right back where they started. It's inconsequential storytelling at its worse.)

The only criticism that can be levelled at Halo and Sprocket is the length of the stories. Maybe the best format is to keep the stories short, without trying to drag out the humour. But as our caring for these characters grows, it's likely that a desire for longer, more involved narratives will develop. Just as long as Callen avoids a "Special: The Origins" issue...