Flowey had full control of Sans, Flowey was laughing insanely as Sans was forced to move because of Flowey's vines, Sans was basically sobbing but Flowey didn't care, You just stood there in shock

Flowey: "Heh, What's the matter smiley trashbag? Have you learned that you're not in control of yourself now?"

Sans: "Kid....Run..."

Flowey forced Sans to raise his arm preparing for an attack as Flowey grinned sinisterly and Sans was sobbing