What is a possible immediate effect of high radiation exposure?

High radiation exposure can lead to a number of immediate effects on the human body, and nausea or vomiting is one of the most common acute symptoms. This can occur due to the body’s response to the damage caused by radiation to the cells and tissues. When the body is subjected to high levels of ionizing radiation, it can cause cellular injury, including effects on the gastrointestinal tract. The nausea and vomiting are part of the acute radiation syndrome (ARS) and typically manifest within a few hours after exposure.

In contrast, the other options suggest positive or unrelated effects that are not supported by scientific evidence. Radiation does not lead to increased intelligence, improved physical fitness, or enhanced vision; rather, it typically results in harmful biological effects, particularly at high levels of exposure.