Original: Doctors used forceps during his birth that severed a nerve and caused paralysis in parts of Stallone's face, resulting in his signature slurred speech and drooping lower lip.
Simplified: During his birth, doctors used forceps, an instrument that looks like a pair of pincers or tongs, that damaged a nerve and caused paralysis in parts of Stallone's face. The paralysis caused his well known slurred speech and drooping lower lip.