You're in the mood for empathy, there's blood in my pen
A metaphor for the pain and heart he puts into his music. If you need someone to relate to or feel for you, he puts the life experience, blood, sweat and tears ‘in his pen’ — i.e into the music he’s created.
“Blood in my pen” is a euphemism for an erect penis and this lyric refers to the intense emotional experience of sexual intimacy.
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