What do animals do as an alarm signal?

Answer 1

It really depends on which animal you're talking about. Some animals make themselves look bigger and/or fiercer, for instance dogs snarl to show their teeth to the enemy and raise their hackles to appear larger; cats make their tails thicker. Many animals (and birds) make a particular noise to warn of danger - barking, growling, hissing, twittering, are some examples, & a classic is a meerkat 'sentry' which makes a noise to warn the rest of the colony of impending danger. Some creatures remain silent but emit a smell to act as a warning or an alarm.