Check every drawer in the kitchen. Check the cabinets and the pantry - it might be with the canned goods; we’re both absentminded enough to put it there. Check the dishwasher - no there’s no reason for the can opener to be in the dishwasher, but it’s not anywhere else, so it won’t hurt to look. Check under the couch - we were using it as a beer bottle opener the other night, remember? Might have left it out there. Well, I don’t know, then. You can open the tuna can with one of the steak knives. Just be careful.