I found some translations on the web.
It seemed that KJW (Rachel) said something that made ShinHye laughed very hard, not sure what it was though, it is not audible.
Later LMH got up to get ready for the shooting, but both LMH and KJW came back to the table when they had to delay the shooting due to the surrounding noise and they started to talk about blood group. It seemed all at the table except KJW are of blood group A, she said her blood group is B, I think. (Bona's A and KT's older brother's O)
So ShinHye turned around to tell PD that she made an amazing discovery, that all of them (not sure if she know Rachel is
are of blood group A. And the PD said he too! ShinHye was amused at the coincidence.
Yes, SH is the kind who could link one event or thing to other, which is why, I guess, she laughs when others don't. I still remember a BTS of Heartstring where she laughed uncontrollably at something JYH said, while he just watched in amuse.