Freaking out the boy

My son and I were eating pizza for dinner last night. My daughter was at her mom's house at the time. After dinner I was going to be heading down to the basement to work on assembling the computer desk for the "library/craft room", and I didn't want to forget the screwdriver so I had it sitting next to my plate.

Son (with pizza halfway to mouth): Why's the screwdriver there?

Me (smiling an evil smile): In case I need to kill you.

Son (frozen, mouth open, eyes big): ... uh.

Me: Hahahahah. Just kidding.

Son: You're just not right.