The term “Son of Sam” refers to the nickname of serial killer David Berkowitz, the subject of a notorious murder case in 1978.
Emilio saying that he’s like a serial killer in the sense that he murders the other rappers in competition (figuratively speaking).
A sonogram is an image that shows how a signal varies with time. So he’s saying that he seems himself as a serial killer with a gun in his hand. Cold blooded!
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