The CDC line about bacteria moving in under 1 second gets thrown around a lot, but I don't buy that it means every dropped cracker is a gamble. A dry cracker on a dry kitchen floor barely picks anything up. Your cousin in Fresno probably got sick from something else she ate that day and the cracker just got blamed. Wet foods on wet surfaces are a different story, sure, but the 5 second rule being flat out wrong for EVERYTHING feels like a stretch.

This is the same thing as when a guy at work tells you to skip the dentist because "teeth clean themselves." People trust the guy who's been doing something for 30 years even when his method is just old, not good. Cheap tires, used brake pads, "you don't need an alignment" - it's all the same penny wise, pound foolish stuff. Your uncle saved you maybe $200 up front and it cost you $410 later plus a scary moment with your kid in the car. Telling him is gonna sting, but he needs to hear it. Just keep it simple, tell him what happened on I-40, and let the story do the work.