It is a traditional instrument of Nepal, known as a "Sarangi". A Sarangi is made up of wood or bones, and traditionally the tails of horses or ponies were used for the strings.
Manakamana is made up of two words - Mana and Kamana. Mana means heart, and Kamana is desire. So, it is a temple where all the desires of our heart is fulfilled.
In Manakamana, it is believed that the sacrifice of livestock to the deity would impress her. Superstition of course, but in Hinduism, sacrifice is a prime protocol.