Interesting question, and here are my thoughts regarding it.
How do the animals act like animals: You have the obvious answers (they live outside) and then there is the not so obvious answer. The animals act in the manner animals are supposed to act, i.e. the pigs are greedy, the horse steadfast and loyal, the guard dogs protective and mean, etc.
Their ideas, and I'm not sure of the nature of your assignment, so you may already know this, but their ideals parallel communism, which was a purely human invention. The pigs are all based on Soviet leaders and act accordingly. Napoleon (Stalin), Snowfall (Trotsky), Squealer (Molotov), and Old Major is a cross between Marx and Lenin (note how his skull is put on display by the others). The pigs overthrow and regime is a parody of the Russian Revolution, with the animals acting in for the various groups.