1. Mooshak(mouse) is not vaahan of Shree Ganesh. Shree Ganesh has got victory over mooshak and in actual scriptures you will find Ganesh's foot is lying over mooshak which means the Lord has demolished the evil. As the Lord Nataraj moorthy stands on daitya apasmar. As Maa Durga's one foot is on Mahishasur. This is the symbol of Lord's Victory over the evil. 2. Mooshak is the symbol of mann(Indriyan) As the human dances according to his/ her indriyan. And Lord Ganesh has got victory over indriyan/ mann. 3. Mooshak or asuras like ravan hiranyaksh hiranyakashyap mahishasur are like our mann only. Our mann always disturbs us from the path of enlightenment. Therefore, the Sadguru swayam Parambrahm takes the form of Mahaganapati Sadashiv Nrusimha Durga and destroy the evil form mann. 4. The mooshak surrendered to the Lord Ganesh after knowing Lord's divinity and prayed for mercy and to be always be with him showing people as symbol of Lord's victory over evil. Just like mahishasur prayed to Maa Durga and bhairavnath prayed to Maa Vaishno devi to be with them so that people must understand Lord's power. This is called sayujyata with Lord. Also as ravan surrendered to Lord Shiv after Lord destroyed ravan's proud. Our mann is like that mooshak ravan. 5. The vaahan of Shree Ganesh are Mayur & simha that's why Lord is called Mayureshwar and Simha Ganapati. Lord takes various avatar in different time interval and chooses vaahan accordingly.