Question about The Exorcist?

People say that the spider-walk scene was disturbing, but I watched the version where all she does is flick her tongue out even though I heard of a different one where blood comes out of her mouth(that I can't find on YouTube). Why do people find this scene so scary? I think it looks cool and in the version I watched, thought it was kind of funny when she started chasing the women around. So yeah my question is why people find it so scary because before i watched it, I thought she like did back handspringsor something but apparently not.