It's probably not surprising to hear this, but McDonald's french fries contain way more than just oil, potatoes and salt. In fact, McDonald's fries have a whopping 19 ingredients in the USA, all of which are broken down in this image:
You may be thinking to yourself, wait a minute! Why are some ingredients listed on there twice? Well, sometimes an ingredient is used more than once in the process of creating fries. Ex-Mythbuster Grant Imahara tells us how french fries at McDonald's are made in this illuminating video:
Items 2-9 are used to partially fry the french fries at the start of the cooking process, whereas items 13-19 are the oil used to fry the fries a second time, at the actual restaurant. Items 5-7 are responsible for the signature McDonald's french fry flavour. And at least one of these ingredients has been "approved for use" in various foods, something that is mentioned to reassure the viewer, but actually only makes me raise my eyebrows a little more.