When it started to show that Tobari had secrets i pretty much concluded that she was a Pheonix. The color pallet and form of her hair screams "FIRE!". So when you do secrets+fire bird the result will be Pheonix almost every time.
Yuki being a Yuki-Ona was the most obvious thing since EP1. Her color pallet and ice patter given it away, and with Hoshino-sensei's hankerchief having ice crystal patters anyone would conclude that Yuki was his wife.
They've already experienced first-hand several times why you shouldn't mess with certain things, but they continue to do it and get surprised when shit happens.
It's like getting shocked when you put your fingers into the outlet and be surprised to get shocked when you do it for the second, third and fourth time
The "Preservation Treatment" makes blood turn into cotton when exposed to air. With that you can't bleed to death, as shown with Kinko when she cut off her hand.
It also makes reattaching limbs easier, but not 100% guaranted. If the cut is too rough or the limb is destroyed, a prostetic is needed. (There's artisans that work making prostetics to players)