菇凉你铁石心肠坚强吗
[gū liáng nĭ tiĕ shí xīn cháng jiān qiáng ma]
Here, ‘iron heart’ describes a hard, almost emotionless state of being but also refers to the girl's toughness and ability to endure challenges. This could either be self-description or a comment to someone else who appears unyielding.