Stuck on Tomb Raider Anniversary

Start by shooting a centaur to maximize its ferocity bar; the first time, they will give you a green glare that turns Lara to stone. To avoid this, you need to roll sideways when they see green.
Next, charge the ferocity bar to the max so a centaur charges at you; dodge it in bullet time (directional arrow + roll).
Get a headshot (shoot when the target is red and not before), the centaur will be knocked out and you will have a few seconds to use the grapple to remove its shield (by pressing interact).
Do the same with the second centaur.
Charge the ferocity bar of a centaur again so it casts its green glare; use one of the shields to send its glare back (by pressing interact behind a shield), quickly release the shield when it turns to stone to shoot it. When it runs out of energy, it explodes. You need to repeat this process as many times as necessary.
Do the same with the second one.
Be aware that if you charge too much, you will turn to stone; they will launch fireballs that you need to dodge by zigzagging.

And there you go, my buddy...

I have the same problem, only when one of the two horses freezes I can't remove its shield. Please explain to me why the grappling hook doesn't latch on.