Buy 2 identical 20 oz bottles of mountain dew. Empty one (you can drink it or dump it, users choice) and completely rinse the bottle with distilled water. Proceed to fill the empty bottle with urine (this can be your own or any type you prefer). With an eye dropper add 7 drops of Drano. Recap the bottle, rinse under the facuet and place in the refrigerator. Tell no one what you have done.
Take the the sealed bottle, rinse it under the facuet. Open the bottle completely, administer the 7 drops of Drano then put the bottle cap back on. Place bottle next the the other bottle in the refrigerator.
After 4 hours if both bottles are still in the refrigerator undisturbed remove them and set them at opposite ends of the dining table. Set a timer for 120 seconds. Call in your wife. Let her pick a bottle and you get the remaining one. Tell her you are having a drinking contest that begins once the timer goes off.
Each of you drink the contents of bottle until it is empty. Once you BOTH have finished your bottle guess who drank what.
At this point you know if you drink the urine or the soda. If you drank the soda ask your wife how hers tasted. If she answered anything other than horrible, and i cannnot stress this enough she can only say it tastes horrible or disgusting, than she is a liar and is likely seeing someone else (if she says it tastes like piss, sh!t, horse piss or anything else you should be aware that she has done this before and is almost certainly involved with another love interest).
Heres the kicker, if you drank the pee shes completely unaware. You dont need to tell her unless you want to, otherwise you have a funny little joke to yourself, and shes probably leaving you for someone better like all the others did.
Howard it is imperative that you dont forget to include the Drano.