Running that code with the second line alone works fine for me (Perl 5.6.1).

I suspect that your problem is that the use of shift in the map *destructively* processes the @foo array -- shift pulls the first element of the array out of @foo, so when you go to do the shift trick again, you're processing an empty array. You can see this if you add the following code after the first 'interleave':

my $foo_size = @foo;

print "\nThere are now $foo_size elements in \@foo\n";
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In this case, warnings told you about something very important!

perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n"; *other_name = *rose; print "$oth
+er_name\n"'
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