Girlfriend said she's a predator and I'm her prey. What does it mean?

She was sitting astride me and held my wrists down while she said that, refusing to let me go. Also, just before she overpowered me, I somehow admitted I liked being bossed around by her. She said she may take advantage of that, haha =D
And then she said the predator prey thing and refused to let me go for quite a while and kept teasing me a little.
What means being "her prey"? Is that a good thing? ;)
Girlfriend said she's a predator and I'm her prey. What does it mean?
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