Gresil: it seems to me that it indeed is a threat: if black ignores , he'll run out of liberties before being able to connect:
unkx80: Oops, your attempt is not quite right. Please try again.
MrTenuki: Well, tenuki is always an option, because this is not a threat :-)
Let's try to solve this by the brute-force method...
After , white is in atari. If white connects at a, black plays
at c and connects. If white plays
anywhere else, black captures two stones at a and connects. And if
is played anywhere else, black will play
at
and connect.