What could possibly make a 3 year old, when handed a sip cup (that you CANNOT see through) say to his 2 year old sister, "HA! HA! I have more juice than you!"?--And then she, hysterically crying, falls to the floor and has a fit.
Is it our fallen nature?
Is it the influence of older siblings?
Is it for no other reason than to drive a mother insane?