To kill a shark's child

I had a dream yesterday night. Wei and I dived to the bottom of the ocean and, believe it or not, there was a hut like underwater station with glass potholes. I was briefed on our mission only after we got into the hut - to kill a shark's child. As we spoke, the great white shark circled around our hut in a frenzied chase after something. Wei shut the door and gave me my weapon - a multi-nozzle hose-picture your garden hose with three nozzles. He said, "You hold this gun, and wait at the door. When they are close, you shoot at the thing that the shark chased. It's his child." With those words, he donned his wetsuit and oxygen tank and face mask and swam off. I was alone in the hut in hellish fear that the big jaw would break in at any time. But then it occurred to me that I was going to kill the shark's child. But why? Isn't cruel to kill someone's child? When Wei came back, he was upset I had done nothing. I asked him. "Why are we killing the shark's child? Isn't that brutal?" Wei looked at me, his small eyes zooming in, "because the shark doesn't have a child."