I have 2 17 week old kittens, Murphy and Olly. Murphy is really friendly and runs when I call on him and pushes his face into my hand to make me stoke him. My other kitten, Olly won't come when I call him and although he does sometimes let me stoke him and sleeps on my knee. However if I put him on my knee or pick him up he always wants down, he also sometimes spits at strangers. Is this a behavioural problem or just his personality. Is there some way I can make him more comfortable with me?