The Dugs had one of the most unique physical appearances of any species in the known galaxy because of their specialized limb structure. Dugs have four extremities; two arms and two legs like all humanoid species. However unlike just about every other humanoid race the Dugs often use their arms to walk and their legs to grapple and/or climb, essentially what most species might do with their hands the Dugs do with their feet.
The Dugs are incredibly talented climbers using all four of their limbs which them to move at amazing speeds through the trees on their home planet.
- Selbulba on Wookieepedia