possesed sans is just flowey but if he posessed sans by controling him with his roots, sans can only say things like "please no" as flowey controls him to do horrible acts.. such as harming his own brother, there are some downsides to possesing sans though, flowey often sits on his eye and his eye sometimes goes badtime mode wich lights him on fire, it dosent kill flowey or harm sans though, the roots on sans are whats controling sans, and the roots are floweys roots