Mr. Bump has already told the Elite Three his plan.
Now, the plan had already  started.

WITH YOONA AND LUHAN

"EHM, err, Luhan-ssi? Can you please explain ...... (some random things) ?" Yoona asked Luhan.
Luhan just nod and began explaining it. Then, Yoona excused herself, saying she's going to grab a glass of water.
Again, Luhan agreed. Yoona went with an evil smirk plastered on her face..

WITH SEOHYUN AND KYUHYUN

Doing the same thing as Yoona did, Seohyun got near Kyuhyun and ask him to explain some random things in the house.
Kyuhyun agreed. Then, while Kyuhyun was seriously explaining at her, Seohyun (with purpose) acted to accidentaly spill her juice over Kyuhyun's pants.
She wants to laugh seeing Kyuhyun's startled expression.

WITH KRYSTAL AND MINHO

While her two partners making progress on the plan, Krystal also made a huge progress. She finished designing - and making - a kind of prank on Minho's bedroom. That time, Minho is still eating (and he eats REALLY SLOW)
So, when Minho came into his room, the trap - or prank - or plan, began to work.

LUHAN'S POV

It has been 1 hour! Where on earth has Yoona been to? Now I'm starting to get worried...

KYUHYUN'S POV

Seohyun really make my blood boil!!! CALM DOWN KYUHYUN!! CALM DOWN!!! She didn't do it on purpose.... Right?

MINHO'S POV

OH. MY. GOD. THIS IS A DI-ZAZZ-TER. AND IT'S FREAKING HOT! MY FEET'S BURNING!!
You see, when I walk to my room, my feet touches some kind of liquid. Hot liquid. BOILING liquid.
Then, I saw that I just step on a pan with boiling water inside. Immidiately I shouted in pain - it IS painful!
Who did this?!!! ARGHH I HATE THIS DAY!!

YOONA'S POV

Somehow I felt guilty upon seeing Luhan's worry face. But a part of me was happy because the plan work.
Mianhae, Luhan-ssi! It's for your own good, hahahahaha!!

SEOHYUN'S POV

WOW, Kyuhyun-ssi is such a fast learner. He even forgive me.. Even I do it on purpose, hihihihi..
Or maybe he didn't notice me doing it on purpose? WHATEVER IDK! Just look at his face!! Hahahahahaha!

KRYSTAL'S POV

OMIGOD! Minho-ssi's face was totally PRICELESS! Hiahahahaha.... it's that hot, isn't it? Well, I made it really hot!
Wait until I tell Yoona and Seo about this.. We'll laugh together!! HAHAHAHAHA!