What is the result of a bed bug feed?

When a bed bug feeds on blood, it begins to swell due to the blood it has consumed. This feeding process allows the bug to increase its size significantly, making it more noticeable after its meal. The swelling occurs because the bug's body expands to accommodate the blood, which is rich in nutrients that are critical for their growth, reproduction, and overall survival.

The other options do not accurately describe the physical response of a bed bug during and after feeding. For example, a bed bug does not become flat or colorful as it feeds, nor does it become invisible, as these descriptions do not reflect the biological changes that happen during feeding. The primary and observable result of a bed bug feed is indeed that it becomes swollen.