----Widow's Wine Perk----
If you stab a zombie or flyer, it gets stopped and chewed on by spiders. This effect overrides instakill if it triggers, this web effect won't happen continuously, it has a short reset timer before you'll get the effect from a stab again. You can be out of 'charges' and it will work, it does not use a charge for this.
Note that the regular knife (not BK) does more damage if you have W'sW.
Your grenades act like charges for the perk. Getting spider drops from WW kills replenishes these charges on a 1 for 1 basis (maybe a couple charges?). You get 4 when you buy the perk, and grenades normally replenish at the rate of 2 per round.
Getting hit triggers the charge, as does simply throwing a grenade (semtex-like). Flyer hits don't trigger the charge.
If you gather enough spider drops, they change red (xbone) or get black spider symbols (360: Now red tinted).
I'm currently unsure what red drops do.
Ragdoll says that it causes the zombies heads to explode when they hit you, if i understood correctly. I have not seen this effect on 360. I feel it may give more charges, or be more powerful, but it's not clear.
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Tips: to keep the last zombie alive while you do stuff, you may throw your grenades away to stop the effect should you get hit.
You can stab a zombie to get the spiderweb effect and gain a moment's peace for box hits (or something else).
If you are out of 'charges', you can try to stab a zombie for the spider effect. Then he may drop a Spider Drop to replenish a charge (or more?).
You can walk into a zombie crowd, the first hit will stop most of them, get hit 1-2 more times (with Juggernog) and then fire the Apothicon Servant and collect the Spider drops/repeat.
You can use Blast Furnace, then pull out a WW Semtex and hold it as the zombies burn and it will turn to WW effect and likely will drop spider drops.
Opinions: Varied, from "it's useless", to "it's okay at times, but annoying", to " OMG, it's a life saver".
You may want to avoid W'sW during early set up to avoid killing the last zombies.
Find it's value in your playstyle and treat it accordingly. But don't expect everyone's opinions to reflect your own.
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Edit: If you have the Bowie Knife and get W'sW, your knife visually returns to standard knife. If you get the BK after W'sW, it will appear as the BK. I believe it is only a visual glitch, no effect, but I'll keep an eye on it.
Edit: This last bit changed in a February patch: now, your camo'd BK turns basic silver when you buy W'sW, but stays the BK.