Hehe, I think @KaMaria was wondering about the same thing some time ago. Here's why: in ruby, when the last argument to a method is a hash, then this is a so-called options hash and the `{` and `}` can be left out. So e.g. `foobar(x, :foo => bar, :baz => bazz)` is the same as `foobar(x, { :foo => bar, :baz => bazz })`, just that the first form is a bit nicer to write and read.

Now, `collection_select` is special, because not only for its last argument it expects a hash, but also for its _second last_. See http://api.rubyonrails.org/classes/ActionView/Helpers/FormBuilder.html#method-i-collection_select . To make sure that the `:class => 'form-control'` ends up in the last argument `html_options` and not the second last, `options`, you must pass an empty hash for `options`.