The Lernaean Hydra was raised by Hera to kill Heracles. Heracles went to the swamp the Hydra was dwelling, and confronted the beast in its own habitat. He started cutting off one head and realized that two grew back. Only one of the heads of the Hydra was immortal and this was its weakness. Heracles was not able to kill the beast on his own so he called his nephew Iolaos for help. He came up with the idea to cauterize the stumps once a head was cut off. Both went to confront the Hydra. Heracles slew the heads off and Iolaos cauterized the stumps. Hera didn’t like what she saw, so she brought another beast into battle, when she noticed that Heracles and Iolaos could win the battle. The crab she summoned got no chance against the hero, and Heracles was finally able to seperate the immortal head of the Hydra from its body, with the golden sword he received from Athena.
The sentences in Kanji Odyssey has many heads as well. One you just cut off, a word you learned, and two others that grow in its place. There are three ways to kill the beast. The easiest is to cut off one head, regain strength, and come back to try and take care of the rest. This means ignoring the words you have to learn and just move on. The second is to create cards for the words not yet learned, and review them along with the others. Or by creating multiple cards testing the unknown words. The beast will still be wild but it will loose some strenght. And then there is a third way.
When there is more than one word in a sentence that hasn’t been learned yet, we can do the following to make it easier to review. Add the word in Hiragana next to the word in kanji, use Furigana for the word until it sticks, put the word in Hiragana only to the front of your card, or use Furigana for the whole sentence, except for the word(s) you learned up to this point. All these options will do the trick to make reviewing easier. There is also a fourth way, that combines the best of both worlds.
Consider that you will learn the word(s) in a sentence yet unknown at some point in time. You can go the extra mile and add the words once they are coming up in a sentence as vocabulary card. Add the Hiragana or Furigana to the front of the sentence card, and try to remember the meaning of it while you are reviewing the sentence. The fourth option is to add the deck model for vocabulary cards to the sentence model, add audio for the unknown word(s), and the word in kanji with furigana. When you review the sentence you will reinforce the words and are likely to remember them. You will hear the word once, you can read it, and you hear the word again once you flip the card, to see if you got it right. Remember that you will learn the words anyway, so you have less work later on.
When you review the sentences rate it according to the known words you have learned. Once the unknown words stick you can go and remove the audio, the Furigana, and keep only the word in kanji. I hope that this will help you as much as it helps me to speed up reviews and making them a bit easier.