I was trying to read a text file each of whose lines should contain two whitespace-separated fields. I wrote the file so I know it has two fields per line, but it's better to be cautious, so I decided to check that it's indeed two fields. I wrote this. 

while (<>) {
    2 == (my($x, $y) = split " ") or die "wrong number of fields";
    ...
}

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That gives the error 
wrong number of fields at -e line 1, <> line 1.

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despite that line 1 of the file really has exactly two fields. Why? Solution under the fold.
<Reveal this spoiler or all in this thread>

In reply to Surprise: scalar(($x, $y) = split) by ambrus

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