$ perl -le 'print STDOUT foo'  # bareword
foo
$ perl -le 'use strict; print STDOUT foo' # strict disables barewords
Bareword "foo" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.
$ perl -e 'use strict; sub foo { }; foo' # works fine
$ perl -e 'use strict; foo; sub foo { };' # error, foo is a bareword, because it's not declared yet
Bareword "foo" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.
$ perl -e 'use strict; foo(); sub foo { };' # that's where you actually need the parens; no error