We adopted MIL's 2 older cats when she went into care earlier this year. It is going OK- they are troopers and very resilient and I think have settled in well. However they seem to be on a killing/present giving spree, escalating towards Christmas. In the last week they have killed 2 mice and 2 birds, each time laid out neatly on the carpet.
How can I let them know that we know they are grateful?