Shrike is, naturally, likewise being very careful. What if he pulled too hard and the rope caught on one of Grant's teeth or something? So he tries to gauge things as best he can, pulling only a little bit harder than he feels it pull back, if he can.

Not that it's particularly obvious that's what he's doing, of course. Probably the only real indication to an observer might be that he doesn't appear to be putting that much effort into it, perhaps.