Thought you'd like to hear about the boys' latest hobby - jumping out and surprising us with a tremendous "boo!" Usually it happens when one of us is coming home. The boys hide behind the kitchen wall and the parent who is already home asks the arriving parent to inspect the oven or look in the sink or check the fridge and then when they get over to the right side of the kitchen the at-home parent says the "code word" (usually something like "Welcome home Daddy") and the kids jump out from behind the wall and collapse into hysterics.
Sam is getting old enough, however, to recognize that perhaps Steve and I aren't quite as frightened as we may appear. The other day Ben jumped the gun and gave his "boo!" when I was still pretty far away. Although I thought that my frightened performance was quite compelling, Sam wasn't going to be fooled and turned on Ben with an angry, "Oh, Ben, you blew the whole thing! Don't you get it, she's only pretending to be scared!"
That's why we had to institute the codeword rule, so that Ben knows when to jump out. His timing is getting better with practice, I have to admit, although the practice element means that getting surprised is routine whenever you return home... which does make it a bit less of a surprise.