In most of recent Japanese comics, character's voice(and non-verbal voice such as inward thought) is written in a balloon. There are some rules, and one of them is "to finish conversation done in one panel within one round trip". That is to say, assuming that there are two persons(A and B), A shouldn't speak again basically in the same panel in which A first spoke and B first replied.
It may be hard to understand with only language, for example;
("YOTSUBATO!" vol.7 p36)
In the right panel, the girl replies after utterance of the man, and in the left panel, the man says after laughing of the girl. The sequence of their communication has two round trips, and it is separated into each conversation in two panels so as not to be written in one panel. This is the concrete example.
This rule exists for not to break down the multilayered structure of time in one panel.
To begin with, what is the multilayered structure of time ?
When you say something, time same as your having said it passes, of course. In regard to the quoted example of the right, when the man says "Yoshi ja-a itterasshai, kiwotsuketene", time same as his having said it passes(maybe about two seconds), and when the girl says "Wakappaaa !!", time same as her having said it passes(maybe about a second). That is, time including their utterances, three seconds at least, passes in this panel.
In addition, each speaking characters is depicted at the moment they are just speaking, and they are not influenced by behavior done after their utterances.
("YOTSUBATO!" vol.10 p208)
In this panel, they speak by rotation from right to left(Ena→Yotsuba→Miura). Looks of first speaker, Ena, is depicted at the moment she speaks so, and not influenced by later utterances which Yotsuba and Miura make. Though a few seconds must pass between Ena's utterance and Miura's, Ena keeps her face steady without Yotsuba and Miura's influence. On the other hand, Miura makes her face after listening Ena and Yotsuba's utterances.
From this, I can think that a panel cuts off not only an overall view of one point on time axis but an arbitrary expression of each objects between arbitrary two points on time axis, and pushes those expressions into itself. It is a forcible way, in a sense. In the above panel, Ena is depicted with her own time, Yotsuba and Miura are in the same way. They are not depicted with the identical time.
There is differnt time on each characters in one panel. It is the meanig of the multilayered structure of time. Though a picture is an instantaneous expression, once it is placed in a panel of a comic having utterances, complex phases of time occur in it.
Well, if a author draws a character twice in one panel without any explanation, we may think "Oh, he/she is a Japanese Ninja". It has to be avoided to draw the character whenever he/she makes any utterances. In other words, though a character says more than two time in one panel, he/she must be depicted just once. So, because charcters stop their time when they primarily say something, they must say second utterance with looks they makes at first utterance, notwithstanding passage of time.
Situation has changed, but looks haven't changed. This is the breaking down of the multilayered structure of time.
The multilayered structure of time causes unnatural situation that utterance and looks are in discord. To avoid it, we adopt the rule which is "to finish conversation done in one panel within one round trip".
But everything has the exception.
To answer the demand for drawing the exception, there is other rule which make us feel no unnatural even though we read conversation done in one panel more than one round trip.
However, it's not so difficult. Formaer rule contributes to avoid "unnatural situation that utterance and looks are in discord", so you should depict the situation seen natural even though conversation more than one round trip is made.
First, don't make a situation that looks at second utterance differ from these at first.
("YOTSUBATO!" vol.9 p99)
In this panel, we don't feel unnatural. Still To-chan, the man who is to the right most, speaks even three times. Because his looks made at first utterance are valid as second and third utterance. His a little bit stern looks with suspicion contain no wrongness which utterance he says, first, "Koitsu-wa-aho-nanoka", second, "Ikura-sun'no?" or third, "Aho-ka".
("YOTSUBATO!" vol.10 p138)
Also in this example, Asagi, the long-haired woman, and Yotsuba, the girl who tied up hair, speak twice, the former in the right panel and the latter in the left one. Their looks are suitable for either first utterance or second. In the left panel, I can even say it is funny because of Yotsuba's content looks.
Like this, you can avoid unnatural situation by contriving a conversational context which doesn't need change of Character's looks,or which unchange of Character's looks brings about some meanings.
But if you want to make conversation which differs from that, which contain the context changing character's looks in one panel, adopt this rule.
Second, you don't depict character's looks from beginning.
("YOTSUBATO!" vol.9 p64)
To-chan first explains calmly, but at the second utterance, he speaks loudly listening to Yotsuba's words. Looks at first utterance should be depicted calmly, and the second angrily. But by being depicted from behind, that is, by not depicting looks from beginning, two different looks coexist without problems.
Of course, there are many exceptions. Conversation more than two around trips in one panel is often depicted without these rules. So we should grasp it not as rule but hint.
well, considering rules behind works is interesting, isn't it?
original article in Japanese:『よつばと！』から考える一コマ内の会話のルールの話 - ポンコツ山田.com