This is an urban myth. It’s true that putting Mentos into a bottle of Coke will cause an impressive geyser of soda to erupt from the bottle. However, you won’t get the same effect from eating Mentos after drinking Coke. The eruption you get when you mix Mentos and Coke is generated by the rough coating of the candy, which causes lots of bubbles to form rapidly on its surface when it’s placed in a carbonated beverage. But the rough coating of the candy begins to dissolve the moment you eat it. So you won’t get the same reaction in your stomach.