Answer:
Put into a pit, locked beneath a grate, guarded through the night, yet it still goes out.
It stands upright and can be quite grand. Its secret is not hidden but right at hand. What is it?
Voiceless it cries, Wingless flutters, Toothless bites, Mouthless mutters. What is it?
Long and slinky like a trout, never sings till it's guts come out.
Pregnant every time you see her, yet she never will give birth.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?