|text= '''Dean:''' How come she didn't die when I stabbed her?<br>'''Henry:''' Because demons can't be killed by run-of-the-mill cutlery. At the very least, you'd need an ancient demon-killing knife of the Kurds.<br>'''Dean:''' (Pulls out Ruby's
Knife from his jacket.) That's what this is.<br>'''Henry:''' (Shocked.) Where'd you get that?<br>'''Dean:''' (Puts the knife back.) Demon gave it to me. We've been around this block so many times.
|author= [[Dean Winchester]] and [[Henry Winchester]]
|source= [[8.12 As Time Goes By]]
The knife has has been used to kill demons and hellhounds. It
The white-eyed demon [[Alastair]] was immune to the knife's killing power
,<ref name="four09" /><ref name="four16" /> However [[Sam]] noted at one point that Lilith herself was scared of the knife,<ref>[[4.02 Are You There God? It's Me, Dean Winchester]]</ref> and she continually took precautions to avoid being stabbed with it whenever confronted with it.<ref>[[3.16 No Rest for the Wicked]]</ref><ref>[[4.18 The Monster at the End of This Book]]</ref>
Crowley, too, has always avoided being stabbed with the knife
,<ref>[[5.20 The Devil You Know]]</ref><ref>[[6.10 Caged Heat]]</ref> . While Crowley stated in [[10.22 The Prisoner]] that the knife couldn't kill him, this may have been a bluff as he was later shown to be nervous in its presence when Dean pulled it on him after disabling him with an [[angel blade]].<ref>[[11.02 Form and Void]]</ref>
[[Image:Ep20 rubysknife.jpg|350px|right|thumb|Detail of the engraving on Ruby's knife.]]
===[[5.20 The Devil You Know]]===
[[Sam]] uses the knife to try to kill [[Crowley]]
- and slices into the [[Impala]]'s rear seat when the demon disappears. He makes another attempt, but is again unsuccessful. Later, [[Dean]] takes the knife and uses it to kill a [[demon]] protecting [[Brady]]. [[Sam]] eventually uses the knife to kill [[Brady]].
===[[5.21 Two Minutes to Midnight]]===