$ perl -we'@foo = 1..10; for (@foo) { delete $foo[10-$_] } print scalar @foo'
5

$ perl -we'@foo = 1..10; for (my @bar=@foo) { delete $foo[10-$_] } print scalar @foo'
0
$ perl -we'@foo = 1..10; for (@foo,()) { delete $foo[10-$_] } print scalar @foo'
Use of freed value in iteration at -e line 1.