**Core Concept**
Pinocytosis and phagocytosis are two types of endocytosis, a process by which cells internalize molecules or particles from the extracellular environment. Both involve the formation of a vesicle around the substance to be engulfed, but differ in the size and composition of the substance.

**Why the Correct Answer is Right**
Pinocytosis involves the internalization of small molecules or fluids, whereas phagocytosis involves the engulfment of larger particles, such as bacteria or dead cells. However, both processes share the common feature of forming a vesicle around the substance to be internalized, which is essential for the initiation of endocytosis. This vesicle formation is mediated by the actin cytoskeleton and the assembly of various proteins, including dynamin and clathrin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not true for both pinocytosis and phagocytosis. Pinocytosis typically involves the internalization of small molecules or fluids, whereas phagocytosis involves the engulfment of larger particles.

**Option B:** This option is incorrect because it is not a characteristic that is common to both pinocytosis and phagocytosis. While both processes involve the formation of a vesicle, the size and composition of the substance being internalized differ.

**Option D:** This option is incorrect because it is not a feature that is shared by both pinocytosis and phagocytosis. While both processes involve the internalization of substances, the mechanisms and pathways involved differ.

**Clinical Pearl / High-Yield Fact**
A key distinction between pinocytosis and phagocytosis is the size of the substance being internalized. Pinocytosis typically involves the internalization of small molecules or fluids, whereas phagocytosis involves the engulfment of larger particles, such as bacteria or dead cells.

**Correct Answer:** C. Both involve the formation of a vesicle around the substance to be engulfed.