Instead of breathing fire, the Thunderdrum produces a strong concussive sound that can kill a human at close range. The blast is so powerful that the dragon is said to "get its power from Thor himself."
Legend also has it that when a Thunderdrum hatches from its egg, it makes a sound so loud it rattles the sky!
See more of Thunderdrum in:
Book of Dragons
Dragons: Defenders of Berk
Dragons: Riders of Berk
How to Train Your Dragon 2
Strident and assertive, the loud Thunderdrum always makes its feelings known
When not swelling up with air in order to yell, Thunderdrums can actually flatten their bodies by expelling all oxygen from their massive lungs for a limited period of time. In this sleeker state, Thunderdrums can better skim the ocean surfaces or even dive beneath the waves in search of prey!