He is taken by surprised by the abrupt behaviour of the boy.

One minute, he seems to be enjoying his mother's attentions. The next, he is coming towards him shouting.

He gets up to react (though not before noticing that the kid is blessed judging from the size of the bulge in his pants).

"Sit back down!" he growls, raising his fist as he moves in on the boy.

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Everyone has a dark side. This is mine.