Dereferencing will get you the value contained in the scalar reference, but the spec expects the package name. The code

print "a $$class goes ", $class->sound, "!\n";

will yield the output

a Mr. Ed goes neigh!

not the expected

a Horse goes neigh!

It will also fail outright if the code is invoked statically, with the error under strict:

Can't use string ("Horse") as a SCALAR ref while "strict refs" in use