The phrase 'by instinct' describes actions or behaviors that are performed without conscious thought or reasoning. Other ways to convey this idea include phrases such as 'reflexively,' 'by nature,' 'spontaneously,' 'intuitively,' and 'instinctively.' When faced with danger, animals, and even humans, often react in a way that is automatic, triggered by their natural instincts. Certain verbs, like 'react,' 'respond,' or 'act,' can be used to describe these instinctual behaviors. Additionally, words like 'innate,' 'inherent,' 'intrinsic,' or 'natural' can also be used as synonyms for 'by instinct,' emphasizing that the behavior is part of something's inherent nature.