UPDATE: No, actually it does die. This is not a warning. Observe:

   $ perl -e '@names = (["Nan Tregar"], ["Sam Tregar"]); eval { @names
+ = sort { $a->[0] <=> $b->[0] } @names; }; print "ERROR WAS: $@"'
   ERROR WAS: Sort subroutine didn't return a numeric value at -e line
+ 1.
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-sam