Extract common words from two/more csv files

Shell Programming and Scripting
1

I have two (or more, to make it generic) csv files. Each line contains words separated by comma. None of words have any space. The number of words per line is not fixed. Some may have one, and some may have 12... The number of lines per file is also not fixed.

What I need is to find common words between two files. A word that may appear somewhere in line 5 of first file, can be in line 21 of second file.

Example:
File 1
----------

word1
word2, word1, word3
word6, word7

File 2
-------
word9, word10
word11, word1, word2
word12

2

Try:

awk -F ',[ \t]*' 'NR==FNR{for (i=1;i<=NF;i++)A[$i];next} {for (i=1;i<=NF;i++)if($i in A)print $i}' file1 file2