If your furby thinks it shaking while in the vertical position and switches its personality to evil/Feisty/ Viking mode. The furby tilt sensor is broken or too sensitive. For instance, if the furby dances, he may stop, since he thinks he's being shaken. I advise to take apart the furby to clean/replace his tilt sensor
This site might help even though it's for older Furby's:https://furbytech.tumblr.com/post/167541924614/how-to-clean-a-tilt-sensor
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