Fa Sang Jeung

Fa sang jeung....peanut butter! that's what I had stuck in my head. In the midst of my thoughts was this single word. I really don't understand how such a random word can fit in with the thoughts of the day. What's even crazier, I never spent any effort trying to remember this word: it was just one of those words we came across in our food chapter in Cantonese class. How can my mind remember such an inconsequential word and not remember the essential phrases I need in the moment I need it. Maybe it's just doing its job... sticking to the roof of my brain! Now, how to get that to happen to the other words I need to know...