Used in a variety of ways, this trope is when someone is forced to react to some unexpected action, such as being tossed something, or facing an unexpected attack. This can be used to see if they are faking being left- or right-handed, or to determine if they are Obfuscating Disability (such as by kicking or stabbing a supposed paraplegic in the leg). Of course, sometimes it's just a way of seeing if someone is paying attention or not. Often an Invoked Trope.
- In the original Buffy the Vampire Slayer movie, this is how Buffy's watcher reveals that she is the slayer, by throwing a knife at her face. She catches it inches away from contact.
- The Brady Bunch. When a man claims whiplash in a minor fender-bender with Carol, Mike proves that he's faking during a court appearance by loudly dropping his briefcase. The man instictively turns to look at the loud noise, disproving his claim that he can't move his neck.
- Life: Someone is going after extremely wealthy lottery winners, and one of them has gone so far as to hire a bodyguard. Crews tests the bodyguard by unexpectedly throwing an apple at him; he is taken unawares, which demonstrates that he's not a real bodyguard. He's the perp and has been holding his "client" hostage.
You are not a very good bodyguard, you know that Robert? I've been watching you. All you do is watch your client. That's why I got you with that Pippin there. You're supposed to watch everybody else, that's where the threat is coming from. Didn't they teach you that in bodyguard school? So, I'm thinking, if you're always watching your client, then maybe the threat is coming from your client; but what kind of threat could your client be? ... You're not really a bodyguard are you.
- Batman. Bats tests a very fat sultan by surreptitiously poking his backside with a long letter opener; the fact that he doesn't react shows Batman that he's not really the fat sultan, he's The Joker in disguise.
- A story arc in the fifth season of Babylon 5 centers around Garibaldi falling off the wagon and becoming an active alcoholic, while trying to hide it from his friends and colleagues. Zach suspects this, and offers Garibaldi an orange, getting his attention before tossing it to him. Garibaldi fails, clumsily, to catch the orange, and Zach confronts him about his suspicions.
Hello, Unknown Troper. You'll need to get known to lend a hand here.