However, if you look REALLY close, you'll see that the boy, although cautious, doesn't seem to mind The Instigator overly much. The smile becomes true and full of play... and he keeps coming back for more.
I can't tell you HOW many times I've said to these two (well, mostly The Instigator) if you don't KNOCK IT OFF, I'm going to separate you!!! 
Maybe one of these days I'll be able to hide my smile as I reprimand them and actually mean it...