The Mindflayers have placed a tadpole inside Boo, knowing he is the brains in the pair.
Minsk, having lost not ONE, but TWO witches, is desperate to save Boo, and joins your group in that endeavor.
Boo, having learned the Speak with Animals spell, casts it frequently on Minsk, enabling the group to converse with and understand Minsk, who of course - while unpetrified in body - remains "stoned" in mind.
Ultimately, you learn that Boo is in fact, the Absolute, and has been planning his rise to Godhood and conspiring with the Ilithids and the Evil 3 since the end of BG2.
