I personally don't like the snarl. For someone dressed like an animal, I'm okay with it, but for a human / formerly human / undead human character I don't like it. It's too simple, and it's unimaginative. Now for some undeads, like zombies, it makes sense. But if you're using something so simple, chances are there's a hundred other scareactors doing the same thing. Now put yourself in the guests' shoes. Would you want to go through 5,6,7,8 attractions where even a quarter of the scareactors are snarling? I wouldn't. It gets old.
That's why Sam, and The Bouncer before him, doesn't/didn't snarl. Sam has a set of different things he'll say to or ask the people that walk past him. If it's busy and there's a long line of people coming through, sometimes he'll do the Sam Slam and glare at you while he resets so that he can get the people later in the group (because, after all, the Sam Slam is the most effective scare tactic that he's ever used), but if he's out and talking, he's not snarling. He's saying things that are unique to him, things that no other scareactor is saying because he thought long and hard to come up with those lines.
So to all scareactors and future scareactors, be creative. Sure, it takes time to think of things to say. And some things you find will work, and some won't. It's trial and error, but after a few times you'll find out quickly what doesn't work, so you drop those and continue to use what does. I've even found that my improv skills have improved over the years. Sometimes a guest will say something to Sam, and Sam will come up with a snappy comeback. Or Sam will think of something a few minutes later and use it the next time someone says something similar. It just takes time and some thought.