>perl -e"use strict 'refs'; ${'foo'} = 1;"
Can't use string ("foo") as a SCALAR ref while "strict refs" in use at -e line 1.

>perl -e"use strict 'refs'; &{'foo'}"
Can't use string ("foo") as a subroutine ref while "strict refs" in use at -e line 1.

>perl -e"use strict 'refs'; goto &{'foo'}"
Goto undefined subroutine &main::foo at -e line 1.