Answer:
Pregnant every time you see her, yet she never will give birth.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.
Round as a button, deep as a well. If you want me to talk, you must first pull my tail.
Stealthy as a shadow in the dead of night, cunning but affectionate if given a bite. Never owned but often loved. At my sport considered cruel, but that's because you never know me at all.
Useful tool for who in darkness dwell. Within you, corrupting like a deadly spell.
I am a animal that is cute but dangerous, what am I?