ON...
'(<a href="http://www.j-archive.com/media/2005-03-10_DJ_22.jpg" target="_blank">Sarah of the Clue Crew shows a chalkboard diagram.</a>)  A <a href="http://www.j-archive.com/media/2005-03-10_DJ_22a.jpg" target="_blank">line</a> that continues in its own direction, it's also part of this expression for where some people go when talking'
on a tangent