Shakespeare's "Sonnet 129" is an extended hymn of self-loathing. The general tone is one of righteous anger at past sins and desires, maybe not the kind of anger one would see from a cat trapped in a tiny cage, but still pretty vicious nonetheless.

Although the sonnet is written in a somewhat impersonal manner, it's clear that the speaker is referring to himself. He positively loathes himself for all the stages of lust he's passed throughout his life, and how he succumbed to his desires at each and every turn.

Lust is longing "past reason"; it drives us to do things that are completely irrational. And the speaker is positively ashamed to admit that each time he fulfilled that longing it immediately became something shameful. No sooner is each lust fulfilled than it is despised. And the speaker clearly despises himself for his actions. Yet despite this he has maintained the same pattern of behavior right throughout his life, never learning from his mistakes.

As one reads the sonnet one can almost imagine the speaker hissing and spitting at himself, just like a cat in a small cage. He's absolutely furious at his own behavior, what it's done to him, and how it's made him feel.