Fear of the Unknown
If you were abducted, put on a spaceship, brought to another world, and told that you would be eaten alive, wouldn't you be a bit worried? By classical human nature, Dr. Ransom is a bit scared when this happens, but eventually learns to accept that there is nothing to be scared of on the planet Malacandra. The planet has people on it just like Earth - they just happen to look a little different. Ransom eventually becomes friends with the people there, likely because he was not forced to do it - he consciously made the decision to befriend them.
Difference
When Ransom is brought to the planet Malacandra and sees slim figures walking towards him on water, he thinks that the end is near. But, as it turns out, these are nice people that do not want to harm him. Ransom helplessly flees into the forest - if they truly wanted to, they could have followed him. When Ransom sees a creature at a lake in the forest that speaks to him in a structured language, he says to himself that this may be a good creature to spend time with. In this case, Ransom still follows traditional human etiquette of bonding over similarities - not differences.
Fact and Fiction
When Ransom returns to Earth, he is smart enough to know that no one will believe his story. However, it was so real that he had to tell someone. Even if it was a dream, was it really not real if it happened that precisely? He confides in his former student Lewis to talk to about the planet Malacandra. Lewis actually asks Ransom about a word in an ancient Latin text, and it turns out it was a word that Ransom had heard on the planet. That means it had to have happened - right?
