The first time you feel a baby move inside your body, you think, "Dang, those tacos are acting up on me." The second or third time, you think, "Wait, what was that?" Tapping? Fluttering? Does lunch flutter? Then, there's the first distinctive thump. And you think, "Ohhh," and recall with amusement the previous taco/lunch incidents.
I am pretty sure something is thumping around in there. And even though I have experienced this before, it is still a surprisingly sweet, alien experience.