radical
Eye, the indexing radical, the left of a doubled pair of eyes on top. The two eyes picture a startled creature glancing sharply about, the root of the 'alert, vigorous' sense.
semantic
Eye again, the right half of the doubled eyes. Two eyes side by side intensify the image of darting, watchful looking.
semantic
A short-tailed bird, sitting below the eyes. A wary bird with darting eyes is the original scene the whole character draws.
semantic
A hand at the bottom right, reaching to seize the alert bird, completing the lively, energetic image.