According to one member of SS501, tickling is the one thing one must not do to HJ -- those who dared got a beating. MM must've been informed either by someone close to HJ or HJ himself about it and naughty MM, I guess, wants to see for herself if she would get the same fate as others in the past. But, luckily no harsh reaction from HJ. Good boy!
In this scene, MM's character was suppose to tease HJ's character about being jealous with BJG
but the two became too playful and MM tried to play rough. hahaha
Payback time -- it turned out MM is ticklish too. hahaha
Cr. as tagged.