The eagle remains motionless for most of the poem; if you're like us, though, you imagine him turning his head from time to time to look around. You know the eagle has tremendous strength for its size, and Tennyson knows that you know this. We've all seen eagles or comparable birds in action. The poem builds suspense by playing on the expectation that the eagle will perform some amazing feat of acrobatics or descend on some poor rabbit or fish…any moment now. But instead, the eagle takes a swan dive off the cliff and allows himself to "fall" far below. The eagle of course achieves this with almost effortless grace. Great vision, powers of flight, and big talons: the eagle must have been first in line when the eagle was assigning skills to all the animals.
The poem shows how exceptionally strong individuals often look awkward and bizarre to more ordinary individuals.
The eagle's strength manifests itself at the end of the poem as pure energy. To borrow an expression from physics, the poem converts the eagle's potential energy to kinetic energy.