For instance, say Ktulu wrote in a normal thread she was trying to strangle Ophelia, you would roll the dies as normal. If the roll + Ktulu's attack was greater than Ophelia's defense, then the magic worked and Ophelia would be strangled. She can still write that she's trying to get away and run, or you could even say she wasn't strangled and fell and hurt herself that way trying to get away (i.e. same as in battles your damage needs to be taken but you can determine why you took it) - at no point does that force Ophelia to fight back.
Assuming though Ktulu's attack + the roll was not enough to beat Ophelia's defense, then she takes no damage, as in normal fight threads, and can escape freely.
Maybe I'm just not understanding?