Are there any negative health effects from eating a bunch of hard McDonald's fries?

No. I suggest you chew them well. Your digestive system will do its best to process them. It will not scratch your stomach.

The negative health effects are not caused by the hardness of the fries remnants, but from the fats and and sugar used to prepare the fries. So yes, there are “negative health effects from eating a bunch of hard McDonald’s fries”.

If the fries are crunchy hard then they might scratch the enamel of your teeth.

It’s junk food, of course it’s bad for you. In small portions, no biggie though. If you like the crunchy leftover shit at the bottom of the carton, have at it and don’t worry about it.

Chew them well & I’m fairly confident that you’ll be just fine!!! Now, the rest of the meal may not be that good for you. Apparently the food is filled with preservatives. This article shows a pic of a McDonald’s meal that had been put in storage for 24 years. It looks hard but has not rotted nor degraded in any significant way. I wouldn’t even be willing to taste those fries!!!

Hard fries that you describe can scratch the inside of you mouth or scratch your gums. Not a major heath problem but it can be annoying.

Not that I can even imagine.

No.

Only if you don’t chew them first.