Arild, I am sure that the children in the neighborhood have lots of stories to tell about the man on their street who shot Pumba's grand father
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I have seen this kind of damage several times on different kinds game but always when the bullet placement is in rear, I call it the "popcorn" effect. I think it happens when the bullet tunnels under the dense muscle flesh and forces it upward in an eruption... I have a difficult time explaining it though the picture shows it well.
It's great that you took that picture, we often don't think about taking pictures of these unusual kind of things that happen, but it's interesting to see and talk about.