What does as nervous as a long-tailed cat in a room full of rocking chairs mean?
If you were a cat with a long tail how would you feel about
having all those rocking chairs that might run over your tail?
You'd be really nervous.
It means that person is very nervous because a cat with a long
tail in a room full of rocking chairs is in great danger of getting
its tail crushed by one and so it is nervous and twitchy.
Think about it. A cat with a long tail would be afraid that one
of the rocking chairs would squash his tail if he wasn't careful.
Careless cats sometimes get stepped on. This is similar because
unless the cat's careful with his long tail, it will more than
likely get squashed by one of the rocking chairs.
You would have to think of the scenario to understand it.
Imagine you are a cat. Cats are good hunters, and as such, they are
naturally jumpy. Now rocking chairs move. A cat with a long tail
would be likely to make the chairs move. The chairs moving would
startle the cat, and reacting, the cat would cause more chairs to
move, and may end up completely terrified. So a person comparing
someone to that is saying that the person is quite nervous or
scared.
This expression uses an interesting image: it compares a person
(in this case, Ted) with a cat, and not just any cat-- a cat with a
long tail, trying to make his way through a room without getting
hurt. Any one of the rocking chairs could land on the cat's tail at
any time, crushing it very painfully and making it impossible for
the cat to move. In other words, the image tells you that Ted is
really ill-at-ease and insecure, just like a cat trying to get
through a room before someone in a rocking-chair catches him by the
tail.
A cat with a longer tail would have a better chance of getting
it "rocked on" from the rocking chair. It probably hurts really
bad.