Both Ron Perlman (Clay) and Doug Jones (Prison Guard) starred in Hellboy (2004) and Hellboy II: The Golden Army (2008).
The book Clay (Ron Perlman) gets at prison is "The Mad King", which is also the title of this episode
Although Charlie Hunnam uses an American accent as Jax, his pronunciation of words often follows the British pronunciation. In this episode the word he pronounces in the British form is "distribute".