Cora is looking at Gotham with a view to tackle. Although he got a bit of a head start she is more lightly built and a little more coordinated so she is a little faster. He, like most boys, is completely clueless he's about to get schooled.
He's still thinking he's out for a harmless family romp with the sisters. Out of the corner of his eye he can see her, "Look, there's Cora! Hi Cora! Wheeee!" Cora has him dead to rights. Zayi is on her way to catch up and since she's the lightest of the three it's no problem.
Incoming. The joy has gone out of his gallop and he's bracing for impact. He knows it's inevitable.
Wham! Gotcha! Going for the shoulder and neck is the best way to take down your prey because it's the centre of gravity. Cora instinctively knows this.
Gotham makes one failed attempt to shake off the predator but it's no use, he's going down. He doesn't stand a chance since Zayi on his other side is honing in to tackle.
And that's it. I'll spare you the carnage of the kill. Today Gotham learned an important lesson: when you have a Ridgeback bitch on your 6 you don't stand a chance.