What's "talking of" mean and when can I use it?

Native speaker’s answer
Rebecca
"Speaking of" is an expression used to introduce a new comment or idea that is related to what was just mentioned. "Tummies" was just mentioned, so the speaker uses "speaking of" to introduce the topic of supper, which can be considered to be related to eating. Ex: A: There was a subway delay this morning. B: Speaking of the subway, guess who I met on the subway yesterday? Ex: A: Look at that cute kitten! B: Speaking of cats, did you know I adopted a stray cat recently?