It's hard to say exactly what happened to the injured cartoon dog. It could have fallen from a height, been attacked by another character, or simply had a clumsy moment and got injured. The possibilities are many.
Maybe he got caught in the crossfire and was hit by shrapnel or bullets. It could be a really tragic situation.
It could be that they were caught in a bad situation like a natural disaster or were attacked by a mean person. There are lots of possible reasons for their injuries.
The injured white haired cartoon boy might have encountered a villain or some sort of perilous situation. Or perhaps he was just clumsy and had a bad fall. We'd need more details to know for sure.
Maybe he tripped and fell. That could cause an injury.
Maybe she fell and got injured while playing nearby.
Maybe the dog got into a fight with another animal and got hurt. Or it could have been caught in a dangerous situation like a fire or natural disaster.
Maybe the dog got scared and tried to find a way out.
The little dog might have wandered off and got lost in an unfamiliar place. Maybe it was chasing something and lost its way.
Often, when a dog bites in a cartoon, it could trigger a series of events like the owner getting worried or other characters trying to help. Sometimes, it's played for laughs and other times for a bit of tension.
The dog might have had an accident or a fight that caused the injury.