How do I create a monster weak point?

Hi all and sorry for my bad english!

I have a monster, this is like a Cyclope.

I would like the bullets were effective only if they hit the eye of the monster .

If they hit the monster in another point, bullets must bounce and the monster not lose energy.

How i can do this?

Thanks to all!

You can pin an invisible sprite on the monster eyes,when this invisible sprite get hit subtract energy from the monster and if the bullet hit the body of the monster make the bullet bounce.

it's hard to say, do the bullets have to go through the monster to hit it's eyes? or are you saying you want to know if the bullet is going to hit the eyes before it happens? so you can then bounce them back if they aren't going to hit the eyes?