It's easy enough to cock a hammer gun in complete silence, as anyone who has used one extensively knows. Just start the hammer back off the safety sear, holding it firmly. Pull the trigger all the way while fully cocking the hammer, and then release the trigger. Gently lower the hammer (holding it firmly) onto the waiting full cock sear and then squeeeeeze the trigger when your sights are solidly on target. It takes far less time to do than to describe, and can be done in absolute silence- even less noise than clicking off a safety on many guns.
Best practice this a lot with an unloaded rifle until you get the hang of it. If you let the hammer slip with a round in the chamber and the trigger pulled all the way back, the rifle will go off just as it was designed to do. Is gun, is dangerous- always be careful. Not something you'd want to do as a routine thing, but it might be useful in exceptional circumstances.
I've had to do this in the field when Mr. Buck was reeealy close... and the range was so short, and my sights already solidly enough on target, that even if my thumb had slipped it wouldn't have mattered. But I've never spooked a deer that was really close with the CLICK of a cocking hammer...
lpl/nc