I'm not a WA lawyer, but I see that no one else has responded to your question. I think that may be because your question is very vague. Are you asking how severe a "bite" must be in order to constitute a case? If so, the simple answer would be that it must be severe enough to cause damage.
It is possible to have a "dog bite" case without an actual bite though. If a dog rushes at a person in such a way to cause that person to fear for their safety, and then the person trips and falls trying to get away from the dog, there may be a valid claim. That's a bit of a stretch though, and would be a difficult case to make without eye-witness testimony.
I recommend you contact a lawyer in WA for clarification.
