ok i get that she was able to get inside rebekah's head, (maybe finn showed her how) or as she said that she needs to be relaxed or whatevr i get that

but damon drinks vervain every day,so he would get used to it,and to prevent the originals to enter his head so how was sage able to see what's in his head??

I don't think vervain can prevent it. We only know that it prevents compulsion, which is not the same. For example, Katherine was able to get into Stefan's head and mess with his dreams, but only Originals can compel other vampires, so Katherine can't, which means that compulsion is harder than "just" getting into someone's head.

yes but at the time both damonj & stefan weren't on vervain remeber in S2 when damon gave katherine vervain so klaus won't be able to comple her.

elena also wear the neclace with vervain so vampires and even orginal vampires can't cople her

LOL, I don't even get how Sage got in to Rebekah's head...

guys forget this,because i talked to my sister and what she said made perfect sence, see even though damon drinks vervain to prevant the originals from compelling him,but sage didn't compel him or rebekah she just entered his mind

^ Yeah, I get that much. But how? She's just a pretty old - but normal vampire. Any vampire can enter the others mind and steal her/his memory?!