Ds1 is 4.3 and talks nonsense a lot of the time, part of his sense of humour I think. But tonight when I told him off for calling his granny silly and sticking his fist out at her, he said 'Oh, now I have to hurt myself because I was rude to Granny...' and started slapping himself on his arm (not hard), then he said 'Oh that's not hard enough, I'll have to do it on the wall', then went and touched his arm to the wall, all the while looking at me (I presume to check out my reaction). It reminded me that he said something similar a couple of week ago as well.
This quite disturbed me though I don't think I showed it... he has never been physically punished in any way so I don't understand where it came from.
Should I be worried about this and how do I deal with it?