Rust traits method overloading (does not compile)

gistfile1.rs

trait BalancedEater {
  fn eat(&self) -> Self;
}

trait CrazyEater {
  fn eat(&self) -> Self;
}

struct CookiesMonster {
  cookies: int,
  hungry_level: int
}

impl BalancedEater for CookiesMonster {
  fn eat(&self) -> CookiesMonster {
    if self.cookies >= self.hungry_level {
      let new_cookies = self.cookies - self.hungry_level;
      return CookiesMonster { cookies: new_cookies, hungry_level: 0 };
    } else {
      let new_hungry_level = self.hungry_level - self.cookies;
      return CookiesMonster { cookies: 0, hungry_level: new_hungry_level };
    }
  }
}

impl CrazyEater for CookiesMonster {
  fn eat(&self) -> CookiesMonster {
    let mut new_hungry_level: int;
    
    if self.cookies >= self.hungry_level {
      new_hungry_level = 0
    } else {
      new_hungry_level = self.hungry_level - self.cookies;
    }

    return CookiesMonster { cookies: 0, hungry_level: new_hungry_level };
  }
}

fn main() {
  let cm = CookiesMonster { cookies: 10, hungry_level: 5 };
  let new_cm = cm.eat();
  println!("{:?}", new_cm)
}