Also, the uses of preservatives, refrigeration and antibacterial agents means that the way food goes bad today is very different than the way food went bad when our noses evolved.

For example, flies circling round meat would make most people instinctively think twice before eating it. In most environments, they will appear within a few hours of the creature dying. In your fridge, the flies won't hatch, taking away a vital signal marking the age of the food.