In this case the GP is making a reference to "The Mote in God's Eye". An alien species has 2 hands that are similar to humans, but they also have a 3rd arm, whi

In this case the GP is making a reference to "The Mote in God's Eye". An alien species has 2 hands that are similar to humans, but they also have a 3rd arm, which leads them to say, paraphrased, "on the one hand, on the other hand, on the gripping hand" since it's strongest.