Mowgli's response is unusual because, until that moment, he has never experienced deep emotional pain or the ability to cry. In the context of the jungle, where he has lived among animals and learned their ways, Mowgli has not encountered the complexities of human emotions, particularly sorrow and loss. His tears indicate a profound change in his identity and a recognition of the reality that he is being disconnected from the only home he has ever known, the jungle.
To Bagheera, Mowgli's tears signify the transition from being a creature of the jungle to becoming fully human. His ability to cry and express emotion suggests that Mowgli is no longer just a "cub" of the jungle but is maturing into a man. Bagheera recognizes this emotional shift as evidence that Mowgli has left behind his innocence and is beginning to grapple with the complexities of human experiences and emotions, marking a significant moment of growth and transformation.