Alan Zukerman and Scott Shapiro wrote:

Could you provide some background on the very perplexing warning that a pregnant woman who walks on a fingernail clipping is in danger of miscarriage?

Wilfred Schuster from Toronto wrote:

What is the origin of the habit of burning one's nail clippings or disposing of them with care? Is there a source for this in the Tanach or in the Talmud?

The ruling that one should carefully dispose of fingernail clippings is found in the Talmud and is cited in the Shulchan Aruch. The reason the Talmud gives for this 'very perplexing ruling' is that a pregnant woman who steps on a fingernail clipping is in danger of a miscarriage. What is the idea behind this?

According to Kabbalah, Adam was created with a hard shiny membrane covering his whole body. When he ate from the forbidden tree Adam lost this covering, but it remained on the tips of his fingers and toes.

This concept is a metaphor for a very deep idea: Every person is intrinsically immortal due to his spiritual soul. However, by attaching himself to the physical world through improper actions (Adam's sin) a person becomes vulnerable to death and material destruction (loss of protective covering).

The concept of a fingernail harming a pregnant woman is based on the following idea: The nail, which is dead matter, represents death and the mortality of the human being. The pregnant woman represents creation, life and immortality. In mystical thinking, objects contain 'sparks' of the ideas which they symbolize. Opposite 'sparks' brought together can cause harm on the spiritual and physical level. Hence, the fingernail, death, is kept away from the pregnant woman, life.

Sources:

• Moed Kattan 18a, Nidah 17a
• Shulchan Aruch, Orach Chaim 260.
• Ibid., Be'er Heteiv