Someone is not sure how to react to what's going on. He smells the new kitty. He feels the new kitty. He hears the new kitty. He hasn't seen the new kitty yet. They take turns roaming the house, smelling places where the other one has been.
Our old and very aggressive cat (aggressive towards "not his people") seems to show no signs of aggression for now, lets me to pet him with the kitten-smelling hands and lets me brush him with the brush full of kitten hair. Believe it or not, in this picture, he is purring - despite of looking rather skeptical.
We will have to think about the best steps to introduce them in the next day. Hoping for the best.