Pterodactyls

Why can’t you hear Pterodactyls go to the bathroom? The answer is quite simple and may surprise you. Individuals suffering from kidney stones, on the other hand, are quite loud, their pain is almost unbearable and shouting helps them endure. The kidney stones become trapped at sites where the ureters narrow along their paths until reaching the bladder. If a stone reaches the bladder, they can be passed in the urine.

Question: Where in the pelvis do kidney stones become trapped?

Postscript: The answer to the riddle is that the P is silent.