There are two references to a song by the band Tool called "Ticks and Leeches." Early in the game look closely at one of the walls. You will see the words "Ticks & Leeches" which references the song. This is not a coincidence, as later in the game, about where the Noosemen appear, written on the wall are the words "Suck Me Dry," which is a phrase constantly repeated in the song. Also, the phrase "I hope you choke" or "I hope you choke on this" can be found written on a wall some time before the gun fight with the guards and the man with the gun turret. This is also part of that song.