Well, they have two kinds of neck-fighting, actually. There's a low-intensity kind where they just shove at the other giraffe's neck with theirs, trying to force the other off balance. The "high intensity" kind is where they haul off and whack each other with their necks.
Now, a giraffe neck has the same number of vertebrae as your typical mammal neck, which is seven, but a giraffe's neck is some seven feet long, which means a chain of big ol' foot-long neck bones. A bunch of muscle is involved in holding that thing up, too.
Turns out there's a lot of weirdness in your anatomy when your brain is ten feet above your heart. A giraffe's heart is about two feet long, has muscular walls three inches thick, and beats 150 times per minute. This means a giraffe has a blood pressure double that of a human's.
There are also a bunch of one-way valves in the veins leading away from the head, so that de-oxygenated blood doesn't rush back to the brain during drinking. And a special complex of blood vessels to moderate pressure changes so the giraffe doesn't faint raising its head after drinking.
It's interesting that the giraffe didn't kick him like they would a pest or predator, but necked him like they do to rivals. Or at least that's the way I'm reading they use the two defense techniques. I could be wrong. Giraffologists feel free to set me straight via email.
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