Ok here's the deal and you have to do this. He'll never forget it....
Go buy some coveralls (yes Pea I'm sure I freakin misspelled it and most of the other words in this post but I don't care) and a hockey mask. Ya know buy the same get up the TX Chainsaw Massacre dude wears. At about 4 in the morning sneak out of the bedroom, put on the get up (the mask is a must!) sneak back into the bedroom, crank up the chainsaw, give it a few good revs and see if he looks suprised

......... for maximum effect put more oil in the gas than recommended (makes for more smoke ;-) )
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Waddya think