yank char by char onto end of search string

[Dan Jacobson]

Gentlemen,
  C-s runs the command isearch-forward...
  Type C-w to yank word from buffer onto end of search string and search for it.
  Type C-y to yank rest of line onto end of search string and search for it.
Yes, but how about also providing a key to just yank one character at a time?!
Indeed, often a whole word is just to much.  Why, how could Stallman
never have though of this?