Thanks to Tze for pointing this out. Further discussion of it doesn't really fit with the thread where I found it, and I think it's interesting in its own right.
We don't really know how the Valyrians trained their dragons. We're told that it could be spells and horns, and other possibilities include imprinting, trust-building, powerful will, whatever. Dany, as we all know, uses "dracarys" as the command for her dragons to unleash fire. It starts as a way for them to cook their own meat, and eventually she uses it to kill her enemies (Astapor) or scare them (Yunkai). We don't know if other Targaryen riders had verbal commands for their dragons, given that people who saw riders would probably be too far away from them to know if they had verbal commands or not.
What's interesting about "dracarys" is that the dragons seem to "obey" the word, not the person.
“Drogon,” Dany said softly, “dracarys.” And she tossed the pork in the air.
Drogon moved quicker than a striking cobra. Flame roared from his mouth, orange and scarlet and black, searing the meat before it began to fall. As his sharp black teeth snapped shut around it, Rhaegal’s head darted close, as if to steal the prize from his brother’s jaws, but Drogon swallowed and screamed, and the smaller green dragon could only hiss in frustration.
“Stop that, Rhaegal,” Dany said in annoyance, giving his head a swat. “You had the last one. I’ll have no greedy dragons.” She smiled at Ser Jorah. “I won’t need to char their meat over a brazier any longer.”
“So I see. Dracarys?”
All three dragons turned their heads at the sound of that word and Viserion let loose with a blast of pale gold flame that made Ser Jorah take a hasty step backward. Dany giggled. “Be careful with that word, ser, or they’re like to singe your beard off. It means 'dragonfire' in High Valyrian. I wanted to choose a command that no one was like to utter by chance."
All three dragons respond to the word, and Viserion actually obeys. And Jorah isn't really even commanding, merely asking a question, which can affect the tone and inflection, and yet they still respond.
Dany wanted a word that no one was going to say accidentally, but as Tze pointed out, Valyrian isn't exactly an uncommon language in Essos. And when you have dragons around, it's not out of the question that someone somewhere is going to use the word for "dragonfire." Even if it's only to say, "Holy shit, watch out for dragonfire."
A verbal command could still be useful if it didn't get out what the verbal command was. But she says the word both in Astapor and when treating with Grazdan Mo Eraz.
So, given that it seems to be a case where the word is important here and not so much the one saying it, what are the odds that someone 1. accidentally uses "dracarys" and causes a dragon to unleash unintended fire, and/or 2. intentionally uses "dracarys" in order to get the dragons to attack an specific target?