Spraying in the house

[Lovingfreedom]

I have two cats, brother and sister 6 years old, both neutered. I've had them a year from car rescue. They are delightful and settled in really well. I'm sure they are generally very happy. In last few days I've noticed a smell which I assume is spraying. This hasn't happened before. I can think of two things that might have upset the male. A bird flew in the house the other day. I was trying to shoo it out the window then my cat saw it and killed it with one blow. I screamed. Had that upset him. Or is it the fact that we served them up food in gravy rather than jelly for two meals and they were both non-plussed?

Could be a urine infection?
My gorgeous cat gets them especially after being stressed.

How many litter trays have you got in the house for them, Loving ?

Do you have a cat flap? May be a stray unneutered tom is coming in and spraying when you're not around. Although there is a difference between neutered tom cat smell and unneutered, so you'd probably know the difference.