" A VIM dancing doll!
function! Dance()

	if &modifiable

		" This variable decides if the main loop is running
		let l:runme = 1
		" Set a mark for us to get back to the line user
		" was working on
		mark L

		" The main loop
		while l:runme

			" Invert the case
			normal Hg~L
			redraw

			" If the user hit a char, then we ought to get out
			if l:runme && getchar(1)
				let l:runme = 0
			endif

			" If we are still running:
			" Sleep a sec to give the feel of animation
			if l:runme
				sleep 1
			endif

			" Undo the reverse-case
			normal u
			redraw

			if l:runme && getchar(1)
				let l:runme = 0
			endif

			if l:runme
				sleep 1
			endif
		endwhile

		" Get rid of the "modidfied # lines"  kind of message
		echo ''

		" Move to the mark, the line user was editing
		normal 'L

	" Not modifiable, Cant run Dance..
	else
		echo 'Can run Dance only on modifiable buffers'
	endif

endfunction

" Command to call the function
command! Dance call Dance()

" Key map to call the function
nmap <silent> <Leader>sv :call Dance()<CR>