If you say it I'm going to kick your ass.
I've actually said Bloody Mary in front of the mirror three times but it obviously didn't work otherwise I'd be in the morgue with exploded eyeballs. Actually I'd be six feet under since it was a while ago. So if you're connected with a death in some away don't say it unless youw ant exploded eyeballs. Also you could end up sending you know who after someone that does so just to be safe don't say it at all.
Sam has a secret so he was able to summon her but now the boys have six hundred years of bad luck with all those broken mirrors. So he actually dreamed about Jessica's death before it happened. It's not like he could have done anything about it. It was a horrible nightmare and he had no way of knowing it would come true.