Speaking in the voice of the Roman emperor Caligula, the poem imagines a ruler stepping out before a crowd and deliberately showing his worst side. "I put on my ugly face" suggests a performance: the ugliness is a mask he chooses, not simply who he is. The line "my last act / conveniently mad" is darkly ironic. Madness becomes a handy costume, something that excuses whatever he does next.
The crow image is the sharpest moment. The speaker compares his violence to a crow arriving to "poke at the people," which makes cruelty sound almost casual, a restless curiosity more than a grand plan. The people, meanwhile, stand "in their fixed / and different pastures," like grazing animals, separate and rooted in place. The poem seems to suggest they cannot band together or move.
The mood is cold, mocking, and a little eerie. The speaker feels detached and contemptuous, even amused, as he looks down at the crowd he is about to disturb.