This William's Blake poem depicts the fearful yet marvelous essence of the tiger along with its traits and also addresses some questions to a God (Probably a Christian one). When the speaker states "What immortal hand or eye, Could frame thy fearful symmetry?", he tries to convey that the sublime, powerful and prominent figure of the tiger (its body) is such that even an immortal being could not contain it, grasp it, frame it.
The "fearful symmetry" clearly refers to the entire body of the tiger. The poem is about God, and is asking whether an omnipotent being could construct such an animal. Thus, the entire animal is subject to analysis.
