This is a link to a chapter by chapter summary of the book. But basically, what happens in Chapter 8 is where the reader sees the interaction between Shawn and his father. His dad puts some food on Shawn's tongue but sometimes Shawn's swallow reflex doesn't kick in and he spits it out like a baby. This makes his father upset. Shawn overhears a conversation about his father just after he left where his mother was telling someone that she understood her husband leaving the family, though she does admit that it was a cowardly thing to do.
The link above goes into more detail and an analysis if you're interested.