Finally, the power of the ratite legs. As I am Wild Emu Guy, I rarely get to handle emus -- they're wild; I can't catch them.
But a couple of times I've had to nurse injured half-grown chicks. The 'drumstick' muscle of the upper leg is astonishingly powerful. It's like spring steel. And a cassowary's legs are substantially larger than an emu's.
Finally, the issue that never gets discussed: why would an emu attack you? I've never been hurt by one of 'my' emus (except Felicity once stepped on me, but that's another story). A Dad protecting his chicks is indeed a scary thing. They will advance on you -- and through binoculars, it's terrifying.
But the point is that emus don't go around attacking people in the wild. If captive, and backed into a corner? Well, that's a different story. My joke about Eric -- the 'original emu' of this project here -- is that I'd rather go three rounds with an hydraulic ice pick than try to stuff Eric into a sack. I've seen him thrash an emu off its feet in a tenth of a second.
Well, then, what about being attacked by a cassowary? I'm glad you asked. As I understand, they'll attack you right off the bat.
So: enormously powerful legs, long evil talon-spike, nasty temper
Does that answer your question?
SE