Explanation
Changing the topic; 'by the way', 'speaking of which'.
Formation
Sentence A + それはそうと + Sentence B
Detailed explanation
The grammar point A それはそうと B is used to change the topic or bring up a new subject in a conversation. It can be translated as 'by the way' or 'speaking of which' in English. It's used to connect two unrelated sentences or ideas, with A being the original topic and B being the new topic brought up.
Examples
Sore wa sou to, kyou no tenki wa ii desu ne.
By the way, the weather is nice today, isn't it?
Eiga wa omoshirokatta desu. Sore wa sou to, kono mise no raamen wa oishii desu yo.
The movie was interesting. Speaking of which, this restaurant's ramen is delicious.
Ashita kara natsu yasumi desu ne. Sore wa sou to, atarashii kafe ga oopun shita mitai desu.
Summer vacation starts tomorrow, huh? By the way, it seems a new cafe has opened.
Kinou no shiken wa muzukashikatta. Sore wa sou to, shuumatsu ni paatii ga aru no wo shitte masu ka?
Yesterday's exam was difficult. Speaking of which, do you know there's a party this weekend?
Practice
Grammar content sourced from hanabira.org.