Blocks become of class Proc in a useful context ;)

blocks_are_procs.rb

class Proc
  def foobar
    puts "...method on Proc!"
  end  
end  

def block_class &block
  block.call
  block.foobar
  puts block.class.inspect
end  

block_class { puts "I'm a..." }
# I'm a...
# method on Proc!
# Proc

blocks are of type rb_block_t while procs are an rb_proc_t, which, as you can see, contains an rb_block_t.