Interesting example, ethanb.

$$Wc
$$+-----------
$$|.X..b1.c...
$$|.....a..O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........
- Click Here To Show Diagram Code
[go]$$Wc
$$+-----------
$$|.X..b1.c...
$$|.....a..O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........[/go]
I think that "a" and "b" are usual replies in this kind of situation (Black stones on the 3d line). "c" is also possible, as are other plays.
$$Wc Sente follow-up
$$+-----------
$$|.X4351.....
$$|...6....O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........
- Click Here To Show Diagram Code
[go]$$Wc Sente follow-up
$$+-----------
$$|.X4351.....
$$|...6....O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........[/go]
White has a sente follow-up, which threatens to kill the Black group.
I think that Black's reverse sente depends upon the ko threat situation.
$$Bc
$$+-----------
$$|.X..5O.4...
$$|.....1..O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........
- Click Here To Show Diagram Code
[go]$$Bc
$$+-----------
$$|.X..5O.4...
$$|.....1..O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........[/go]
If White is komaster, then Black's move is

(or

). Later

-

is sente.
$$Bc
$$+-----------
$$|.X...O32...
$$|.....541O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........
- Click Here To Show Diagram Code
[go]$$Bc
$$+-----------
$$|.X...O32...
$$|.....541O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........[/go]
But when Black is komaster, or often when neither player is komaster, Black has a somewhat unusual play with

-

. (Note that unless White is komaster this normally stops White from going further into the corner.)
$$Wc
$$+-----------
$$|.X...O21...
$$|.....B34O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........
- Click Here To Show Diagram Code
[go]$$Wc
$$+-----------
$$|.X...O21...
$$|.....B34O..
$$|XXXXXXXXO..
$$|OOOOOOOOO..
$$|...........[/go]
Alternatively, Black can play the usual response, and if White plays

, throw in with

.