Bücher der Reihe The Breveny Chronicles

Watch out, dragons... Here be Aaron!  Aaron is a brat, which is understandable after everything he's been through. He also sees dragons when he hums, which isn't understandable by anyone, ever. He soon gets sucked into the dragons' dangerous war, where his only defences are his embarassing magical fingernails, and a fierce, ten-year-old, girl.