On the subway, when people are having conversations in a foreign language and it’s clear that they not only don’t mind eavesdropping but are indeed encouraging it, I like to glance at them periodically, my gaze resting on them just long enough to register that I understand what they’re saying, and match my reaction and facial expression to theirs but on a smaller scale, so they know that I know what they’re saying. Even though I usually don’t. “What? This tiny dark-haired lady understands our Tall Blonde Weird-Vowelspeak?” one probably says as a test. So I smile just in case.