Ever since one of his battle with Eggman the doctor accidently burned his flesh because of a fire on his mech but, when Sonic smelled the flesh he couldn't resist and bit Eggman's hand as hard as he could, tearing his hand off and now he slowly developed a taste for human flesh.

But he did get slower the more humans he at now he's just as fast as a normal car with speeds of 30 mph but he is still deadly and can kill a human even with riot armor 

He does ignore Mobians for obvious reasons 