没再细问，迷信的东西哪里还会有原因？我古狗了一下，还出问题了

According to this, he should give ME a penny :

superstition states that you should give someone a coin when they give you a knife. I've heard two reasons for this. The first says that it is to ensure that the knife doesn't cut the owner; the second reason, which I've heard more often, is that it is to ensure that the knife does not cut the friendship between the giver and the recipient.