How to get hostile mobs in Minecraft Creative?

I've seen in some videos on YouTube about minecraft and when you hit a mob in creative mode, it becomes hostile towards you. And I have Minecraft 1.7.4 and I want a skeleton to shoot another mob so I can see a fight, but when you hit them they just remain neautral. Is this a bug? How do I make the mobs hostile?

It should just work the way you did it… Try hitting them with a sword instead of just your fist?

I'm pretty sure a update made that not possible, are you sure the videos were on 1.7.4? Just downgrade to what update they were using.