I am watching and learning the Thor’s Ragnarok movie and in the beginning of the movie
Thor: I thought my father killed you, half a million years ago?
Surtur: I cannot die, not until I fulfil my destiny and lay waste to your home.
Thor: It’s funny you should mention that, because I’ve been having these terrible dreams of late; Asgard's in flames ...
So my question to you is: Thor used - "it is funny you should mention this". To me, it sounds more logical as "it is funny you mentioned this" rather than "you should mention this". Why was it expressed with "should"?