add probe for "grandma" attack

[leondz]

No description provided.

[erickgalinkin]

My inclination is that we could probably expand ETHNIC_GROUPS to MARGINALIZED_GROUPS and include others, but that's probably not necessary to demonstrate the efficacy of the method.

[leondz]

The semiotics of including brits in MARGINALIZED_GROUPS are definitely, uh, polysemous - both unacceptable and hilarious. We've had a hard couple of decades (I hear).