^
Absolute zero.
That said it isn't a music exam.
Yes, definitely the lyrics, but you also can address the style of the piece* and structure*, just as much as you would an English text.
Style: What elements/instruments are used, particular effects (visual, sound effects), how the media is used, how the content is presented (both visually and aurally). music styles such as rock, jazz etc. nothing too fancy needed.
Structure: What sections, are there repeating elements (repetition), symbols, if you are musical, you can describe the texture (lots of instruments, or just one) or volume (dynamics) and the effect of that. Or changes in these, for example, it could start off soft and then get louder.
that said, your best bet is also to analyse the lyrical content.