Sometimes they look rather less like humans, in which case (if friendly) they often resemble large teddy bears.
Not only do Aliens with Forehead Ridges mostly look like Earth Humans, they tend to act like Earth Humans as well, or at least one particular (real or speculative) Earth Human culture.
It would be expecting much of anyone to guess that an oyster were alive if he came across one (for the first time) with a closed shell.
TRADE with them is sporadic, and even WARFARE seems less frequent than it used to be in the GOLDEN AGE.
We can not only communicate, Trade, and fight, but form joint business ventures, cheat each other at cards, and even fall in love.
Indeed, Aliens with Forehead Ridges raise a profound question in evolutionary biology.
However, Aliens with Forehead Ridges continue to thrive in Hollywood Scifi. In casual encounters with the material universe, we rarely feel any difficulty here, since we usually deal with things that are clearly alive, such as a dog or a rattlesnake; or with things that are clearly nonalive, such as a brick or a typewriter.
This is for an obvious reason: the audience wants aliens of One of the first ways in which we learn to classify objects is into two groups: 1. Nevertheless, the task of defining "life" is both difficult and subtle; something that at once becomes evident if we stop to think. The caterpillar is alive, but the rock is not; as you guess at once, since the caterpillar is moving and the rock is not.