With regards to what animal is cute and has poisonous claws...
The one animal that confounds biologists and give geneticists headaches...
The fuzzy-wuzzy and all-around adorable... platypus.
ADD] With regards to Konata pulling up of her sleeve, this is because it is inappropriate for a lady to show her armpits. Due to her height, Konata suffers from the law of gravity because she has to fully extent her arms to reach the hand-rings. It's a play on the ills she has to suffer for being such a shorty.
Cheers.