That threat, of course, is Bruce Banner.
The film brilliantly utilizes Canada’s vast, desolate wilderness as a chess board. Wolverine realizes he cannot overpower the Hulk. He must outsmart him. The chase sequence through the forests, where Wolverine uses tree trunks as projectiles and lures the Hulk onto a frozen lake, is a masterclass in animation choreography. Hulk Vs Wolverine 2009
Wolverine, despite being a murderous mutant, recognizes a kindred spirit: a man trapped by a monster inside him. When Wolverine breaks into the lab and sees Banner strapped to a table, he says the most important line of the film: "I’ve been in that cage, bub." That threat, of course, is Bruce Banner