Arnold is crossing a chasm via a log bridge. In a tense moment, he realizes the monster is right behind him on the log. In a blink, Arnold is clinging to the bottom side of the log using his big muscles to hold on. I don’t see how he got there silently, and I don’t see how he gets back up on top. Is this an impossible scenario?
Certainly no more impossible than a sentient extraterrestrial big-game hunter with a convenient intersteller pickup truck, a bigger gun than he really needs, and on-demand invisibility.
Clearly, the situation demands suspending more than just Arnold.