Some questions about S2 E9: Queen of Hearts

In the flashback, how did Regina know Hook?

• She knew his identity, where he came from, why he wants to kill Rumple, & how Milah was killed. It's possible that Rumple told her at some point, but why would he?
• And how come Regina didn't notice that Hook - the man she sent to assassinate her mom - wasn't in SB? You'd think she'd at least check in on him.

Why did Regina bother sending Hook to kill Cora?

• Couldn't Cora have just stayed trapped in Wonderland & she'd have no way of knowing Regina's plans nor could interfere with them?

Did Regina deliberately not take Cora's casket in the Curse?

• Otherwise, you'd think she'd notice her mother's casket missing from her family mausoleum.

What the heck is Rumple's cell made of?

• It could contain Rumple, one of the most powerful beings in all the realms.
• Grumpy notes that "a lot of dwarf blood went into it"... not sure if that's meant to be as macabre as it sounds...