The simplest remaining possibility is that $foo is not a person, that your constructor is somehow failing. This could be due to the package not loading. If I were you, I'd enable strictures and warnings and add this line after attempting to create the object:

print "Foo is a ", ref($foo), "!\n";
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You shouldn't have to preface method calls with package names, nor do you need to import anything from Person (so you can safely drop the method name list). Oh, and the double colons are package name separators.