In the second stanza of the poem, the speaker refers to the metaphorical fire of the tiger's eyes. The speaker, addressing the tiger directly, asks "In what distant deeps or skies / Burnt the fire of thine eyes?" The speaker here is wondering where the tiger might have come from, and the implication is that the fire in the tiger's eyes perhaps came from the stars.
Elsewhere in the poem, the speaker uses the fire metaphor to suggest that the tiger might have been created industrially. The speaker asks, for example, "In what furnace was thy brain?" The tiger appears to be so powerful and beautiful that the speaker can't help but wonder how it could possibly have been created. The metaphor of fire suggests that the tiger may have been created from the stars or from an industrial furnace.
The fire metaphor is also used throughout the poem to emphasize the tiger's elemental beauty and power. In the opening line of the poem, and again in the first line of the closing stanza, we are told that the tiger is "burning bright," suggesting that its beauty is so bright as to be dazzling. In the second stanza, the speaker, speculating as to the creation of the tiger, wonders "What the hand, dare seize the fire?" The hand here is the hand of the tiger's creator, and the implication is that the tiger's fire is so bright and so powerful that the speaker, in awe, struggles to imagine a creator's hand powerful enough to contain or manipulate it.