the use of $_ was a 'code to taste' manuever on my part. I use the magical assignments all the time:)
What I saw was the file being printed out, then the while loop trying to print 'yeppers' each time cat was found.
While I was unaware that printing the file stream and then trying to call it in the while would fail, I imagined the output to be the full file printing, and then any number of 'Yeppers' one after the other. I was assuming what he wanted to do was print yeppers along with the text instead of one after the other.