This a good question. There are several places in the book where there are statements of cannibalism. In a real sense, the danger is always present before the reader. In light of this, let me give you a few examples.
First, The mother says these words to the man. The following words are unambiguous and filled with fear. Also it is good to note that there is a sense of confidence in her words.
"No, I'm speaking the truth. Sooner or later they will catch us and they will kill us. They will rape me. They'll rape him. They are going to rape us and kill us and eat us and you wont face it."
Second, arguably the most graphic scene of cannibalism in the book is the description of what the man and boy saw when they entered into a house in search for food. Instead of finding food, they found a group of people huddle in the basement. They were being stored like animals to be eaten - perhaps even breed. I will quote in full to give you a sense of the disturbing image.
"He started down the rough wooden steps. He ducked his head and then flicked the lighter and swung the flame out over the darkness like an offering. Coldness and damp. An ungodly stench. The boy clutched at his coat. He could see part of a stone wall. Clay floor. An old mattress darkly stained. He crouched and stepped down again and held out the light. Huddled against the back wall were naked people, male and female, all trying to hide, shielding their faces with their hands. On the mattress lay a man with his legs gone to the hip and the stumps of them blackened and burnt. The smell was hideous."
The prospects of being eaten alive lingers all throughout the book and the imagery is haunting to say the least.