The Raptortongue is a species of dragon first seen in How to Ride a Dragon's Storm. Though a bit wild, they are trained by Vikings as Spy Dragons, due to their ability to flatten themselves.

Raptortongues are Mountain Dragons primarily inhabiting the Gorge of the Thunderbolt of Thor and the Murderous Mountains.

Traits and Abilities

Raptortongues are one of only two dragons able to flatten themselves completely, the other being the Riproarer. Their general appearance is rather flat anyway, but they can flatten further and even fit under a closed door.

"Raptortongues are most peculiar. They look like perfectly normal dragons that have been accidentally stepped on by a giant and squashed as flat as a pancake. They are often used by Vikings to spy on enemy tribes, because they can fly low and swift and silent without anyone realizing they are there."
How to Ride a Dragon's Storm

How to Train Your Dragon (series)

How to Ride a Dragon's Storm

Hiccup, Fishlegs, and Camicazi are captured by Raptortongues during the Inter-Tribal Swimming Race, then delivered to Norbert the Nutjob's ship The American Dream 2. They are Madguts the Murderous' secret weapons, as suggested by the fact they are found in Murderous Mountains.

How to Break a Dragon's Heart

Raptortongues are also mentioned in How to Break a Dragon's Heart, when Humongously Hotshot slips quietly past them in the Gorge of the Thunderbolt of Thor into Uglithug lands to kidnap Princess Tantrum.