+1 brilliant, asking for the PC to simply repeat a statement. :) I can see this in combination with Command can being very effective with Zone of Truth.

This can still be circumvented easily using the same logic: Eve: "Say the words 'I did not kill King Bob'." Alice: "I did not kill King Bob" (yesterday at two). Since murder took place yesterday at five, Alice can get away with saying that.

@MatejDrobnič "I am not living" and "I am not living there anymore" are two very different statements which start with the same words. Under the spell rules, "I did not kill King Bob" is a lie and I don't see why some non-pronounced words which could be added to the sentece make this legit. Alice would need to say the whole sentence: "I didn't kill King Bob yesterday at two o'clock" to make it truthy, but the unnecesary and unrequested adding is just a proof of guilt. "Excusatio non petita, accusatio manifesta".

"I did not kill King Bob; [a lifetime of poor dietary choices left him unable to process medicinal arsenic]"; "I did not kill King Bob; [for liability purposes, it was the ocean that killed him, not us]"; "I did not kill King Bob; [Paladine called his soul before me]"; "I did not kill King Bob; [he killed himself by his wickedness, and I am no more killer than a hammer is a carpenter]"; "I did not kill King Bob; [the snake I sent down the ventilation shaft to his bedroom did]": any of those may be what an observer would call untrue, but what if Alice truly believes in them, for the time being?

@Rekesoft But spell is subjective based on Alice's beliefs. If, by reframing the question in her mind, Alice believes those words are not a lie, she can utter them.

@MichaelHomer While rationalizations of your misguided deeds are common among criminals ("I didn't kill him, the bullets did") nobody ever truly believes them. You lie to yourself, you know that you're lying to yourself, but you choose to keep doing it because it makes you feel better. You still know it's a lie. If you can claim that your character "really" believes those lies then it's cognitive dissonance it's so great it completely precludes them to function as a normal person - since you can't be insane only when you chose to. That's a -10 Wis, -10 Int for your character.

Does a repeated statement have any truth-value? Is it a lie to repeat something that someone has asked you to repeat, or is it merely saying something you know to be untrue? Do actors lie when they speak their lines?

@Rekesoft I disagree. Especially in the world of D&D. A believer in the afterlife may rationalize their actions as merely transporting their victim from the material plane to another plane. They may even believe that their target is undying or immortal. Did I kill the King? No [, he still lives, just not in his castle or in his body.] There are many characters who may believe that statement whole-heartedly and with sanity.

Re ""Say the words 'I did not kill King Bob'."". I would consider that following instructions, not telling a lie. No intent to deceive, and thus not subject to ZoT. It's like playing Simon Says or when copying someone. If they say "ikegami is a nincompoop" and I repeat that, it doesn't mean I'm lying if I think I'm not a nincompoop. Keep it normal. "Did you kill the king? Please answer with a yes or no." Just like in real courts.

@Pingcode if they can't say it, you can also request them to explicitly state the opposite, that they did kill the king. If they initially refuse (which anyone honestly confessing wouldn't), they will comply under duress - in our reality, torture doesn't work because people will say anything and make up things in order to make it stop, so any confessions extracted that way are very unreliable, but Zone of Truth fixes that and you actually can make them say either "I killed the king" or "I didn't kill the king"; "I know who killed the king" or "I don't know who killed the king", etc.

@ikegami: Instead of "say the words", a better instruction might be "tell me truthfully, in these words, ...". Then you are instructing them to speak a true statement, not just repeat words.

@ikegami: It's up to the DM whether ZoT would even allow you to repeat the words of a false statement. I'd be inclined to rule you couldn't. Otherwise, your pre-trial prep could include your lawyer instructing you: "when asked xyz, instead of answering, just repeat this phrase instead". (Same "I didn't kill the king" words, different reason for saying them, making ZoT too easily beatable, especially when you know you're saying this sentence in order to deceive the questioner.) Part of ZoT's description is "guards against deception"; in 5e that's not fluff but still needs interpretation

@Toddleson Many people here on this world believe in life after death, resurrection or reincarnation. Even for them, the verb "to kill" has a definite, concrete meaning.

@Peter Cordes, Re "Otherwise, your pre-trial prep could include your lawyer instructing you: "when asked xyz, instead of answering, just repeat this phrase instead".", No, that would be intent to deceive. The difference is the secrecy. The jury doesn't know of the instruction. That's the same as the OP's "I did not kill (the chicken)". That's a completely different scenario.

@Peter Cordes, Re "a better instruction might be "tell me truthfully, in these words, ...".", Sure, that works, but it's severe overkill. For starts, truthfully is already enforced. As I mentioned, requiring a simple yes/no answer will do the trick too. (Well, yes/no/I don't know.) It works for actual courts, and it would work here too. That's assuming you have a advocate capable of objecting and redirecting.

@ikegami: It's not overkill when there are people arguing for the possibility of ignoring the question and replying to your own mental question. I think that's silly (obvious deception intended, thus ZoT should block it), but I wanted to come up with something that closes both proposed loopholes at once, to cover the hypothetical situation where both loopholes are real. Also, I like the idea of just closing that loophole in an existing idea with minimal modification.

@Peter Cordes Re "It's not overkill when there are people arguing for the possibility of ignoring the question and replying to your own mental question.", Ignoring the question in a regicide investigation isn't going to go well, and ZoT prevents the lie. (Answering a question other than the one asked is most assuredly presenting a false impression; being deceptive.) Again, lying (not being truthful) is already prevented by ZoT. Saying "be truthful" is completely useless.

@ikegami: I already agree the ignoring-the-question tactic is silly and won't work with ZoT; I'm just playing along with a hypothetical weaker truth-forcing effect. And yeah, "truthfully" is redundant. I included it to rule out any argument that "tell me in these words" could be taken as "say the words" (but you don't have to mean them). You could workshop the phrasing to tighten it up while still not allowing your loophole e.g. "state x, in those words".

@Rekesoft @Rekesoft There are plenty of instances where you can rationalise that you weren't the true cause of death. You poison the handle of a knife - if King Bob takes the opportunity to sieze that knife when your back is turned the fast acting poison will kill him before he strikes. Were you the reason the poison was there? Yes. Could you rationally believe it wasn't you that killed him but his choice to take the knife? Definitely.