Barulho estridente, Nazgûl ou sua besta?

Livro 1, cap.4:

"A long-drawn wail came down the wind, like the cry of some evil and lonely crea­ture. It rose and fell, and ended on a high pierc­ing note. Even as they sat and stood, as if sud­denly frozen, it was an­swered by an­other cry, fainter and fur­ther off, but no less chill­ing to the blood."

Livro 1, cap.12:

"...and from the Rid­ers came a ter­ri­ble cry, such as Frodo had heard fill­ing the woods with hor­ror in the East­farthing far away."

Livro 2, cap.1:

"‘Be­cause they are real horses; just as the black robes are real robes that they wear to give shape to their noth­ing­ness when they have deal­ings with the liv­ing.’

‘Then why do these black horses en­dure such rid­ers? All other an­i­mals are ter­ri­fied when they draw near, even the elf-horse of Glo­rfindel..."

‘Be­cause these horses are born and bred to the ser­vice of the Dark Lord in Mor­dor. Not all his ser­vants and chat­tels are wraiths!"

É o chamado dos próprios Nazgûl. Eles estavam montando cavalos normais até perdê-los no Ford de Bruinen. As coisas voadoras ... não aparecem até muito mais tarde na história.

Resposta curta: Devem ser os Nazggl, não os animais mortos, porque ouvem o som no Condado, quando os Nazgull apenas têm cavalos.