substring_index

I used:

SUBSTRING_INDEX( content, CHAR(13,10), 1) AS heading

to use the first paragraph as a heading for some content. Now I need to output the rest of the content without that first paragraph so I tried:

SUBSTRING(content, 6) AS rest_content

But that isn’t working. What other string function should I use to get the content minus the heading?

What does that mean? An error, the wrong result?