Argument by Analogy: a Friend of Yours Is Convinced of the Influence

Argument by Analogy: A friend of yours is convinced of the influence of the Moon on everyday human affairs. He cites a supposed correlation between crime and the occurrence of a full moon as proof. He even speculates that the gravitational influence of the Moon is the mechanism by noting that it is the gravitational pull of the Moon that causes the tides. "After all", he argues, "as over half a human's weight is water, the Moon must affect the flow of blood in human beings!" How would you explain to your friend that this analogy, between the ocean tides and water in the human body, is profoundly flawed. Are there any alternate explanations for a link between moon phase and crime?