He caught Hermione's quiet snigger as he did manual labour in his best suit and heard the tinkling of the crystal’s in the chandelier when Luna transformed. Although Draco could not see her he imagined her wings had nipped it. Narcissa didn't mind however, she clapped delightedly once more, exclaiming over Luna's sinewy skin and huge open wings. Draco knew his mother had witnessed his grandparents" deaths and so was not surprised that she could see Luna in her new body.