How does this description help the reader to understand how the caged bird feels?

In the poem, Sympathy, Dunbar vividly reveals the experience of being trapped like a bird by explaining the actions that caged birds often demonstrate. Birds in captivity flutter their wings violently, as a reaction to unwanted but repetitive requirement to use those wings to fly to the only place he can possibly fly to: his tiny little perch. The pain caused by every one of those violent fluttering of its wings can be felt each time he longs to stretch those wings out in the open, but is only allowed to sit in the same space doing the same thing day after day after day.