The truth cannot be obtained through pure speculation. Peng Sijue took a cotton swab to sample the four walls of the toilet tube and used a blood protein kit to identify whether it contained human blood or not. Although the toilet was dirty, Peng Sijue conducted it meticulously. There was no human blood there.

“It seems that the murderer did not throw the weapon into the toilet. Fortunately-” Chen Shi began.

“What's fortunate?”

“If he threw it there, you’d have to open the box that stores the excrement and stir it with a stick. It's funny just thinking about that!” Chen Shi couldn't help but laugh.

Peng Sijue rolled his eyes at him “Excrement, internal organs, or bones. To me, it's just a protein composition. The difference is just the composition.”

“A good attitude to have.”

Lin Qiupu called and asked them to come over to eat quickly. Mealtime was only twenty minutes, so they had to be sure to hurry.

Chen Shi washed his hands in the sink and said, “Let’s hurry!”

Peng Sijue yelled from behind, “I haven't taken samples yet!”

“Hurry up. Don't expect this case to be done step by step.”

Peng Sijue still took samples from the bloodstains in the washroom before leaving with Chen Shi.

Originally, the first team planned to send boxed lunches to all the comrades of the second team, but Lin Qiupu wanted to exchange information while eating. He booked out a restaurant in the waiting room for everyone to eat at.

Seeing Chen Shi coming, Lin Qiupu said, “It's 12:00 right now and the plane will take off at 3:00 PM. Eat quickly.”

“Then why did you order this steamed dish? It’s hard to eat such a hot dish quickly!” Chen Shi remarked.

Lin Qiupu glared at him. “Only this restaurant could be completely booked out for us, so don't complain. You can let it cool down a bit before you eat. Let's have a small meeting first. I’ve found the identity of the deceased. Deng Shirong was the manager of an insurance company in Jinan, and he’s also a shareholder with 27% of the shares. He retired this year and stayed in his hometown in Hainan. It was only because the company had an important shareholder meeting that he went on this red-eye flight. Interpersonal relationships are quite complicated and it may not be clear unless we investigate for three days. However, the passengers on this plane aren’t acquainted with him.”

“Has anyone bought insurance from this company?” Old Zhang asked.

“I will continue to investigate.”

Lin Dongxue suggested, “This can be asked during our questioning of each person!”

“Very good, we’ll do that!”

Xu Xiaodong said, “I heard that the passengers are all kicking up a fuss and asking how the police are handling the case since they weren’t questioned the whole morning, causing them to wait at the hotel for nothing.”

“Cases aren’t investigated by the mouth. We must know the status of the scene before asking them anything. Old Peng, can you tell us your findings?”

Peng Sijiue said something about the autopsy. At this time, one of his subordinates chimed in, “Captain, we found out that the person’s wound contained a lot of aluminum powder.”

“Aluminum powder?” Chen Shi knocked on his bowl with chopsticks and stood up. “Everyone, I already know what the weapon is.”

Everyone's eyes turned to Chen Shi and Chen Shi took out the foil knife he folded from within his pocket. “The plane offered a meal on board. It was a hamburger wrapped in tin foil. I tried it and folded the tin foil up into this shape. It can completely pierce the skin.“ He raised his left hand to show everyone the wound on his finger.

“Foil?” Lin Qiupu was a little skeptical. “Foil is so soft. How can it piece the skin?”

“Captain Lin knows how to open coconut with chewing gum and watermelon with a paper knife, right? As long as the speed is fast enough, soft things can pierce the skin.” Chen Shi explained while holding a chicken drumstick on the table. He suddenly stabbed into the chicken leg with the foil knife.

Everyone exclaimed in surprise.

Peng Sijue said, “Yes, non-Newtonian fluids[1] can maintain their original state at high speeds. The most typical example is wet starch, and... Can you stop using my chicken drumstick to demonstrate?”

“Okay, okay, great progress!” Lin Qiupu applauded.

One hand was raised in the crowd and Lin Qiupu asked, “Xiaodong, do you have something to say?”

“Er, is there something wrong with everyone? Isn't tin foil made from tin? But aluminum powder was found in the wound.”

“The composition of the tin foil is actually aluminum.”

“Tin foil is aluminum foil, but it was called ‘tin foil’ over in Hong Kong and it just caught on.”

Many people gave Xu Xiaodong a science lecture. Xu Xiaodong was very ashamed and laughed, “Okay, okay, I learned a valuable lesson again.”

Lin Qiupu said, “If the weapon is this, it must be easy to get rid of.”

“Yes, the murderer can crumple it into a ball and throw it away at their leisure. It may even be...” He picked up a chicken drumstick from Peng Sijue’s plate and took a bite. “Eaten!”

“Shameless!” Peng Sijue accused.

Chen Shi said, “Everyone should have received the meal. You can check who has no tin foil in their garbage bag. Dongxue, did you ask the flight attendants what I told you to ask?”

“I’ve already asked them. They said that many passengers passed by the victim's seat. There were too many people to count or remember.”

“Then leave it alone. Just look for the tin foil. Whoever doesn't have tin foil, we’ll have to question!”

Lin Qiupu had a conjecture. “What about the flight attendants themselves? They can also access the tin foil. What if they committed the murder?”

“If you aren’t assured, check it out yourself. I’ll handle the economy class passengers!”

“Well, I won't bet on a probability. I’ll investigate the first-class passengers and flight attendants! Everyone, hurry and eat. We need to continue working after the meal.”

Chen Shi sat down and Peng Sijue took a look at the aluminum foil. Then, he crumpled it in a ball and said, “If the murderer threw the foil into the toilet after crumpling it up into a ball, the blood may not leak out. It seems that I still have to check it... The protein on the plane!“

“The way you put it is even more disgusting. Can you not say it during the meal?” Chen Shi complained as he continued to eat the drumstick he stole earlier.

“Is it tasty?”

“It's so delicious. You try it too!”

Looking at the empty plate, Peng Sijue had no choice but to pick up a piece of broccoli with his chopsticks. Chen Shi said, “Don't check that stuff yet. Go and borrow a metal detector to look around the places for where the passengers have been and see if the killer threw it away.”

“Also, if there is a fingerprint on the aluminum foil, it can be easily extracted.”

Lin Dongxue came over. “Ah, are we going in the wrong direction? Didn't we say that we found DNA in the nails of the deceased in the morning? Why not collect everyone’s DNA and compare them one by one?”

Peng Sijue shook his head. “The equipment is at the bureau. Even if we don’t count the return trip, the time would be too tight. To check the DNA of so many people, it would take a lot of time. Right now, we can only find the killer and then use the DNA as evidence later.”

After eating, everyone rubbed their mouths and left to work. Chen Shi said, “I’m not waiting for you!”

Lin Dongxue was anxious and ate the rest of her meal in a hurry. She threw away the chopsticks and planned to leave. As a result, when she stood up suddenly, she felt the dizziness she felt in the past wash over her even stronger than before.

Then, the scene in front of her became black and she fell to the ground.

1. A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, i.e., constant viscosity independent of stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid. Ketchup, for example, becomes runnier when shaken and is thus a non-Newtonian fluid.