Humans are the only animals that blush

Charles Darwin called blushing 'the most peculiar and most human of all expressions', and he was right in a narrow biological sense: humans appear to be the only species that blushes — involuntary reddening of the face and neck in response to social emotions like embarrassment, shame, or being the centre of attention. The physiological mechanism involves the autonomic nervous system dilating blood vessels specifically in the face. Evolutionary psychologists suggest blushing signals genuine emotional responses that cannot easily be faked, serving a social-trust function. Attempting to suppress blushing typically makes it worse.

Source: Dijk et al., Cognition & Emotion (2009)