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How closely can a game resemble another game without legal problems

So suppose I'm currently developing a variant of a snakes game for the iPhone, and you decided to call it "snakes".

First, in general, how would you find out if a name's been copyrighted or not? It's probably safe with "snakes" because it's such a common word, and that there's been so many games around (please correct me if I'm wrong), but with some people copyrighting the name "edge", it would be best to be a bit careful.

Second, suppose I decided to go with some name that is guaranteed to be different (e.g EL SERPENTES DE LOS REYES), would gameplay be a point of contention on copyright issues? For example, the tetris game is sort of "copyrighted" at the apple app store, and there was a crackdown on anyone using the word "tris" or anything related to it. However, if there was a game with the gameplay of tetris (or loosely very similar), with the name "BLOXODEREX", can it be liable to copyright/DMCA issues?