Shiva Tandava Stotra...
Because of the conditions in which it was composed. He was triumphantly marching forward crushing every living being that dared to stop him- Ravana was at the height of his powers. Hence he was surprised to see a tall snow capped mountain peak blocking his way. Well, never mind- if the peak did not voluntarily move away from his path he would just uproot it and throw it away.
Except that, there were two beings seated on the top of the peak- Mahadev and Parvati. With superhuman strength, Ravana tried to dislodge Kailash. The peak started to tilt and Parvati clutched Mahadev for support. With the nail of his left toe, Shiva pushed Ravana and he fell down- and along with him, also fell his pride, arrogance and conceit.
As he beheld Lord Shiva in his full splendor and glory, he burst into a composition which mirrored the movements of Shiva's tandava- nritya. Since Ravana was a veena player par excellence, he was also playing the veena while singing. But in the middle, one of the strings of the veena snapped. Ravana was in a fix. he could not stop-since his song was about Shiva's tandava and it would be disastrous to stop the dance abruptly. At the same time, without the veena, it didn't sound too good either. So he wrenched out a nerve from his hand and replaced the broken string with his own nerve and continued as before.
This is said to be the origin of the 'hasta veena' .