In Poem 36 of Attar's Mokhtar Nameh, the 'bird of the heart' (مرغ دل) symbolizes the soul as it escapes the 'narrow cage' of the material world. By shedding physical form and worldly attachments ('departed like an engraving from stone'), the spiritual seeker achieves boundless expansion. The poem describes this transcendence as traversing 'a thousand worlds' with every step and 'a thousand leagues' with every breath, illustrating the soul's limitless capacity and infinite mystical journey once liberated from physical confines.