intall twitter-bootstrap-rails

After watched http://railscasts.com/episodes/328-twitter-bootstrap-basics?autoplay=true       feel bootstrap is so coo.

So i try to install it following the vedio. but i got an error:

cannot load such file -- less
Googled it. Nothing changed.

Checking that vedio i found there was some unfamilair gems when "bundle show" executed.  i executed "bundle show" in my shell, and those gems did not show up. So i added it to my Gemfile's assets set

gem 'therubyracer'

gem 'less'

gem 'less-rails'

#bundle install

#rails s

the error message disappeared.   fuck.

When i wrote this blog, i tried to recur the error by commentting gems above out.  nothing happend. fuck.