Klaus is talking to Rebekah, telling her about Bonnie and how she is always on his mind . The rest is pretty much Klaus giving Bonnie an ultimatum 'choose me or your fire, be mine or you will burn'.
Kat talks about the prank @8:10 but doesn't say who pranks her...in the video of Joseph @ Eyecon he says it was him @11:00....PS Kat and Steve are ADORABLE! I will never ship Beremy but I wouln't mind KatQueen! LOL!