The matter is difficult to put into words. For fear, real fear, such as shakes you to your foundation, such as you feel when you are brought face to face with your mortal end, nestles in your memory like a gangrene; it seeks to rot everything, even the words with which to speak of it. [...]. You must fight hard to shine the light of words upon it. Because if you don't, if your fear becomes a wordless darkness that you avoid, perhaps even manage to forget, you open yourself to further attacks of fear because you never truly fought the opponent who defeated you. (2.56.4)
This could have easily gone under "Themes: Fear." However, Pi struggles here with a particular type of fear: the fear of death. He realizes he must confront this particular fear – embodied, perhaps, by Richard Parker – or it will "nestle in [his] [...] memory like gangrene." Translated: Pi must become Richard Parker's master. Which he does in the very next chapter. Pi starts THE PI PATEL INDO-CANADIAN TRANS-PACIFIC FLOATING CIRCUS, whose sole goal is to train and subdue the deadly Richard Parker.