

Press the pad of your thumb and the end of your middle finger together with some force. It helps to offset the finger to the left side of the thumb (looking down at the thumb). Hold your thumb still, and try to pull the tip of your middle finger down to your palm, until it overcomes friction and snaps against your palm at the base of your thumb.
OP asks how to explain to kids about terrorism:
Guy says kids don’t need to have terrorism explained to them:
Guy provides a reason why kids don’t need to have terrorism explained: they already learn about it in the form of school shooters, who are terrorists:
Guy makes an assertion in the middle of the previous sentence that doesn’t really have much to do with it:
Whether or not that part is true has no bearing on the rest of it. But what his second sentence had to do with the question in that it provided context/an example showing how kids already learn about terrorism.