Is there anything in the five second rule, I thought as I considered the bit of Bombay Mix I’d dropped on the kitchen floor. The rule is a folk model of food contamination and posits that you’re safe eating something you’ve just dropped on the floor as long as it hasn’t been there too long.
According to that Wikipedia article – and advice on the NHS website – it doesn’t have a basis in fact and food that has been picked up for measured short periods of time demonstrably develops the same bacterial growth as that which has been left on the ground for longer.
However, neither source notes whether they also looked at the effect of bathing the samples in saliva, grinding them up and sending them down to sit in a strong acid bath, which is what happens when you eat something. Accepting that bacteria are too small to see with the naked eye, I think I’ll still risk it from time to time in a clean, home environment. However, I suspect the risks would be a little higher elsewhere, especially in areas that have a high throughput of people and other creatures and where you aren’t well innoculated by regular exposure.