Why can't Nintendo just sue Sony for imitation?

[sergiodaly]

the nunchuck is a controller with an analog stick and some buttons... unless nintendo has the patent for analog sticks and buttons... no way they can sue anyone... sony didn't release any design for the so called "nunchuck" so there is no indication that has anything to do with the design nintendo make for their nunchuck... also no one can patent one design of an object to be used by humans if that patent don't allow fair competition between rival companies, human have limitations in term of anatomy that can't be patented... no one can have the patent over the general design of a computer mouse if there is no other way a human hand can use such a device...