After you choose C-Team's Poison fragment, you must escape the infirmary.
Seek a Way Out
Get the luminol spray from the desk.
Get the syringe from the bed.
Get the barcode reader from the scanning machine.
Equip the luminol spray and use it on the lockers. Numbers appear on each locker. To unlock a locker, touch it and enter the numbers that the luminol revealed.
The middle locker contains a cube puzzle. Take it, then examine it in your inventory. You have to swap the pieces so that the golden parts are all facing outward. Also, four pieces have small holes on them. These are the top, left, right, and bottom pieces.
Choose Check to try the pieces. If correct, you get a key card.
The locker on the right contains a hint card that says to use the syringe on the candle.
Put the key card into the CT scanner. Use the scanner to scan all three of you in any order.
Afterward, go to the display that shows the barcodes. Equip the barcode scanner, then drag it from left to right across all three barcodes. The locked drawer opens. Get the ink and the lug wrench from inside.
Select the syringe in your inventory, then choose Combine, then drag the ink onto the syringe.
Now equip the syringe and go to the picture of the woman holding the candle. Use the syringe on the candle. If it doesn't work, unlock the rightmost locker and get the note card from inside. After injecting the candle with ink, more candles appear. Use the syringe on both of the new candles.
Now, step back. Then use the lug wrench on all four of the Xs at the corners of the picture. If it doesn't work, you need to step back first.
A container will come into the room.
Go to the lab coat and take the stethoscope. Equip it, then touch the dial on the container that appeared. Slowly rotate the dial to the right, but stop as soon as you hear the click. Then slowly rotate the dial left, and stop as soon as you hear the click. Finally, rotate the dial to the right. The container will open after you reach the third number. If it didn't work, you went too far after hearing the click, so you will have to try again. On the 3DS, you can use the shoulder buttons to rotate the dial more precisely.
Once the container opens up, check on the items inside, and the room escape puzzle will end.
Choose a Letter
After the cut scene, you will have to choose a letter. Re-read the Log to see which letters each person tried. If nobody's tongue tingles/feels numb, the correct answer is the one that nobody tried. If one person's tongue tingles/feels numb, the correct answer is the one that only that person tried. If two people's tongues tingle/feel numb, the correct answer is the one that both those people (but not the non-tingly/numb person) tried. If all three people's tongues tingle/feel numb, the correct answer is the one that all three people tried.