Focusing on "cap":
* trap
* nap
* flap
* sap
* wrap
Focusing on "rodent":
* coincident (not a perfect rhyme, but close and humorous)
* resident
* president (again, not perfect but funny)
Playing with the meaning:
* rat trap
* mouse trap
* squirrel hat
Ultimately, the best rhyme depends on what you're trying to achieve!