Next word is being offered by Word Completion only when next character is a whitespace character (space, tab, newline) or when there is nothing (end of the document) after the cursor.

While this makes sense, when we're in the middle of a word, Word Completion could actually make a suggestion when there's a punctuation character after the cursor and a whitespace character or another punctuation character before the cursor, e.g.:

                           v - whitespace character
    Conducting is an art of direc|.
                        cursor - ^^ - punctuation character, offer next word here

                                 v - punctuation character
    Cetiosaurus oxoniensis was a "prim|", quadrupedal
                             cursor - ^^ - punct. character, offer next word here