"The cat is following the mouse."
Translation:Katten følger musen.
Both are correct and there is now difference in meaning. Bokmål tries to accomodate people with different dialects by permitting different endings. You can essentially choose whether you want to write Bokmål with two genders: common ("-en") and neuter ("-et"); or three: masculine ("-en"), feminine ("-a") and neuter ("-et"). You need not even be consistent.