Maybe you've seen Parelli's Horsenality chart?
(If not, it's also featured in November's Horse & Rider, but unfortunately, the chart isn't in their online edition.)
Well, Jessie over at Jessie and Remington offers a different take on horsenalities.
Click image to visit Jessie & Remington
Sunny is quite definitely somewhere between a 2 and a 4 - after lots of plastic bag work - lol. He's willing to give me the benefit of the doubt most of the time. And of course, the fact that flapping things usually arrive in conjunction with clicker-sessions makes them much more tolerable! (Flapping plastic x tolerance=click->treat=satisfied Sunny!)
Seriously though, a horse that completely freezes under stress worries me more than one that reacts by immediately trying to get away. A nervous, dancing, evading horse is pretty easy to spot. But a freezer is more subtle. On the surface they're handling it. They almost look accepting & quiet (except that they're completely stiff, and the whites of their eyes are showing), but if/when the pressure gets to be too much, they explode. If you haven't read them correctly, it's really easy to be in the way.
The herd has only one true 2: Solitaire. She's definitely a freezer - her mother Diamond was the same way. (Nature vs. nurture, anyone?). Diamond was an old pasture-bred broodmare who never really accepted that people brought anything but trouble with them. She'd accept being caught and groomed, but she didn't enjoy it and she never really relaxed around people.
Solitaire likes people well enough, but when she's anxious she's very, very still. When she was young she was a flipper-over if the stress of being tied & handled got to be too much. She never got loose, and the habit seems to have faded with age. But I don't completely trust that given the right circumstances she wouldn't revert.