What does this word mean? Even though I watch a lot of BBC crime shows, somehow I was not familiar with the term "Grass." I would appreciate it if someone could help me out. Context: He walked rapidly, going nowhere in particular, but every road in Brighton ended on the front. I’m too old for the game, I got to get out, Nottingham; he wanted to be alone, he went down the stone steps to the level of the beach; it was early closing and the small shops facing the sea under the promenade were closed. He walked on the edge of the asphalt, scuffling in the shingle. I wouldn’t grass, he remarked dumbly to the tide as it lifted and withdrew, but it wasn’t my doing, I never wanted to kill Fred. ----Brighton Rock by Graham Greene