1. Why do people, after praying their obligatory prayers, move from their original positions when offering their Sunnah prayers?
Changing positions for performing Sunnah prayers is a sound tradition of the Prophet (upon whom be peace). Just as in the case of Tarawih prayers, the Prophet always wanted to make a clear distinction between what was optional. Therefore in this instance, he ordered the believers to change places, so that it did not look as if the Sunnah prayers were an extension of the Fard. Thus the object of changing places was to provide a deliberate break in between the two. This is also why believers are asked to perform Tasbih in between the Fard and Sunnah prayers - to provide a break. There is a sound tradition from the time of the Prophet which relates an incident where a believer - having finished his Fard prayers - immediately stood up to offer his Sunnah. Omar with the blessing of the Prophet ordered the man to Sit down and wait. With so much emphasis on Fard prayers being offered in the mosque the Prophet advised that Sunnah prayers be performed at home where possible - again to provide a break and also to ensure that peoples' homes were never devoid of worship. "Do not turn your houses into graveyards." he is reliably reported to have said.
(50 - Solah 2)
2. Is it wrong to wear jewellery in the shape of an animal such as snake rings on the wedding finger, or other symbols like the Chinese 'yin and yang'?
It is not advisable to wear, display in the home or exhibit any shape which represents something that lives, whether human or animal. I will cite a Hadith of the Prophet, (upon whom be peace), who warned all those involved in the painting and sculpture of living things. He said that on the Day of Judgement Allah will ask them to breathe life into what they created, but they will fail; they will never be able to that. The prohibition also extends to those who buy and sell such objects and artefacts.
(56 - Clothings 5)