2:06 - The game these two kids are playing is famous in Japan and it's called "Shiritori." You take the last syllable in a word the other person says and start a new word with that syllable. The words can't end with "n" because no word in Japanese starts with just "n." Also, the words have to be nouns and katakana (Japanese writing system, used only in foreign words like konpyuuta[computer] or bonasu[bonus]) is normally not allowed. However, in this case, they do indeed use it.

18:09 - This phrase simply means, "You look like a fool." Literally, the shirikodama is some mythical ball thought to be in one's anus and that if a kappa manages to take it from you, you become a sissy.

24:25 - Lame pun here. "Niku" (meat) sounds like "nan" (what) and so they make a lame wordplay joke.