This is exactly what came to my mind and is how I use the expression when speaking Italian. However, if you gave us more context, it would be helpful, as Azazel said, because one of the other suggestions might fit better!Is it "what makes you say that?" or am I missing some nuance in translation.
Would "how can you tell?" also be a good option?Hi!
Yes, we would definitely say "how can you say that?!"
Hope this helps!