So what's the original Japanese pun?

Alega said:

So what's the original Japanese pun?

From what I was able to read from the last panel it's simply a rhyme: frozun, rozun.

It's worth noting that the "pun" is using English loanwords, so I'm not sure I'd even say that it's in Japanese. As far as I know Japan doesn't have a word for "rose" as it is not a native flower and the English word "frozen" is fairly commonly used, despite Japan having their own word for that.