The other two magic might be confusing but they're not really necessary here. I can still write this and be surprised.

$ perl -we '$n = () = split ",", "one,two,three,four,five"; print "I f
+ound $n comma-separated words\n"'
I found 1 comma-separated words
$ perl -we '$n = ($x) = split ",", "one,two,three,four,five"; print "I
+ found $n comma-separated words, the first of which is $x\n"'
I found 2 comma-separated words, the first of which is one
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And even if I chomp the line, there could be trailing spaces or carriage returns in the line that I expect split " " to cut off.