Actus reus is the act—or the omission or failure to act when there is a duty to act—that comprises the physical elements of the commission of a crime. The actus reus generally must be voluntary bodily movements that constitute a crime.
In contrast, mens rea (meaning “guilty mind”) is the criminal intent element of a crime. It is the intent to commit a crime, or the knowledge that the action, or failure to act when there is a duty to act, will result in the commission of a crime.

In Iowa, as in other jurisdictions, the concept of actus reus requires that a defendant has engaged in a voluntary act, or an omission when there is a legal duty to act, that constitutes the physical elements of a crime. This means that the individual's actions or inactions must be deliberate and lead to the fulfillment of the crime's statutory elements. For instance, if someone is legally obligated to provide care and fails to do so, resulting in harm, this omission could be considered actus reus. On the other hand, mens rea refers to the mental state of the defendant at the time of the crime. Iowa law recognizes various levels of mens rea, including intent, knowledge, recklessness, and negligence, depending on the crime. The presence of mens rea means that the individual must have had a certain state of mind that is required to commit the particular crime in question. For a conviction, both actus reus and mens rea must typically be proven unless the crime is a strict liability offense, where mens rea is not required.