I have a 15 week old kitten, I am also looking after his litter mate of the same age for a week. I have noticed big changes between the two.
I will call my kitten '1' and the other '2'
If I open food from another room 2 will run to me, 1 will not, If I call for them 2 will look at me and his ears will move, 1 will not, If try to get their attention in any way 1 will not react and seems to be 'ignoring' me.
My mum came round yesterday and her keys fell out of her bag to the ground and both kittens reacted, but I assume thats because of the vibration on the ground rather than the sound.
2 will react to his name, 1 does not.
He will be going to the vet next week as I'm having him chipped, but does it sound like he might be deaf? Never had a cat before so for all i know this could be normal and he's just a bit stand offish lol