klupko

1. ball of yarn, thread or string
   Baka mi je dala klupko crvene vune. — Grandma gave me a ball of red wool.
   Mačka se igra sa klupkom konca. — The cat is playing with a ball of thread.
2. tangle; web
   Ta priča je pravo klupko laži. — That story is a real web of lies.
   Pred ispit sam bio klupko nerava. — Before the exam I was a bundle of nerves.
3. (of body posture) ball
   Pas je spavao sklupčan u klupko. — The dog slept curled up in a ball.

The phrase «klupko nerava» means "a bundle of nerves".