Its a different kind of hard, it'll be kind of like cramping. I know for me it starts in my back and.in my lower abdomen (like menstrual cramps in my lower abdomen) and move up through my whole stomach. I can't walk or talk or hardly breath, and while the menstrual like cramps make stay the.other stuff will come and go.
For the most part you'll know, trust me! They are painful. True contractions tend to wrap around to your back as well. Or from your back to your front. There's a huge difference between your belly being hard and a contraction.