Saw itself means saw. If translated directly into saw, the title is not attractive enough.
Maybe it's because the exchange for keeping people alive in the first movie is a chainsaw! The chainsaw itself can split a thing in two. jipsaw called these people together to "play games", hoping that they could accept a test and draw a clear line with the past! At the same time, the past tense of see is saw, which I think should have the same meaning ...
Hehe, this is just my understanding. ...