**Core Concept**
Human milk contains a unique composition of nutrients and bioactive compounds that support infant growth and development. One key difference between human milk and animal milk is the presence of certain nutrients and antibodies that are beneficial for human infants.

**Why the Correct Answer is Right**
Human milk contains a higher concentration of sialic acid compared to animal milk. Sialic acid is a type of sugar molecule that is involved in various biological processes, including cell-to-cell communication and immune system function. The higher levels of sialic acid in human milk are thought to promote the development of the infant's gut and immune system. Additionally, sialic acid has been shown to have anti-inflammatory properties, which may help protect the infant from infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** Human milk does not contain more conjugated linoleic acid (CLA) than animal milk. CLA is a type of fatty acid that has been linked to various health benefits, but its levels are not significantly higher in human milk.
* **Option B:** Human milk does not contain more casein than animal milk. Casein is a type of protein found in milk, but human milk actually contains a higher proportion of whey protein than casein.
* **Option C:** Human milk does not contain more docosahexaenoic acid (DHA) than animal milk. DHA is an omega-3 fatty acid that is important for brain and eye development, but its levels are not significantly higher in human milk.

**Clinical Pearl / High-Yield Fact**
Human milk contains a unique blend of nutrients and bioactive compounds that are tailored to meet the needs of human infants. This is one reason why breast milk is often considered the gold standard for infant nutrition.

**Correct Answer: C. Sialic acid.**