In the episode, Subaru is talking to Rem and Ram about the dinner he ate, and tells the two that it was delicious.
Rem notes that when she showed him that sign, Subaru showed her a sign of his own: a frog.
The official website for the Re: Life in a different world from zero (Re: Zero Kara Hajimeru Isekai Seikatsu) television anime series began streaming the fourth episode of Re:Zero kara Hajimeru Break Time on Tuesday.
Ram is confused, but tells him that the sign he is referring to is one that Rem uses to express happiness.