Guarana heard the hiss, and it saved her, or at least gave her a chance.  She knew that anything about to attack her from behind would likely come in too quickly for her to turn around or jump aside, but her 'summoning' was basically instant.  This was why a splash of ice-cold, eye-stinging liquid went in the general direction of the sound just before Guarana tried to go into a roll.  If she missed completely, she'd look for an opportunity to bite but would probably be done for.  If not, then she'd hopefully get a moment to attack and paralyze a surprised opponent.