The cats sent by the Corinnos to assassinate the twins were used to further Leto's plans, and those plans revolved around Ghanima believing that Leto was killed by the cats. But this seems to imply that there was no real danger at all. Was Leto ever actually in danger, or was he certain that his plan would work?
Leto feels that the tigers represent a real and distinct danger to himself and Ghanima
What will happen out here? he asked himself.
And he knew it would either be death or the play of death, himself the object.
“They may really kill us,” he said.
“This is the chance we have to take,” she said. “We owe it to our father.”
He refuses to use prescience to determine the outcome of the pursuit. Instead he's content to take the risk that they could actually die, for example if they suffer a chance fall, in return for keeping the outcome fluid.
Leto felt that he had stumbled into this place to free himself from his soul. He ran with the sure knowledge that he and Ghanima could reach their narrow notch in time, but his gaze kept returning with fascination to the oncoming beasts.
One stumble and we’re lost, he thought.
That thought reduced the sureness of his knowledge, and he ran faster.
Leto and Ghanima both (presciently) sensed that there was a significant chance of injury to at least one of the twins, possibly even a fatal injury.
“It has to be teased into reach of the knife.”
“Yes, but we agreed that if one of us could avoid being wounded …”
“And you’re wounded, so you’re the one going back,” he said.