// Walk backwards
animation["Walk"].speed = -1.0;

// Walk at double speed
animation["Walk"].speed = 2;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        animation["Walk"].speed = -1.0F;
        animation["Walk"].speed = 2;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        animation['Walk'].speed = (-1.0F)
        animation['Walk'].speed = 2