We used to play steal the log. When everyones had been on compo and saved up for one big dump in the field; the idea was to try and steal it from under him. If you had just squeezed out a large one and looked down to see your handy work and it wasn't there then you would be

It could be done but very difficult unless after dark (use a long handled digging tool). There were all too many failed attempts, though the odd person was quite good at it. What I'm saying is its very difficult to get close, even when the adversary is concentrating on other things.
Then there is different levels of silent. Take .22 LR hitting a rabbit; it makes a real thwack. A kukri, from a full swing, whaack. Rifle butt: thunk. Nothing is very silent unless there is a ghetto blaster on (a diversion of some kind). I'm for pole axing the EN first which takes something big and heavy.
Modern soldiers with flack jackets and helmets don't give much of a target area. Though they may be "made safe" (unloaded, mag on; though shouldn't be). AK types may not even have the safety catch on.
You don't know.
Well placed senties will be doubled up or covered from another position. To take on a sentry, you'd want to be covered. Risky business.
In training, doing the odd snatch party to get an Enemy, is a good exercise, though it takes two to four to overpower one blighter. Its fun, difficult, and shows up close recce faults and sentry positioning well. But thats training.
Going around is by far the best option.