Stubentiger On The Loose

This innocent looking cat was on a serious hunt while I watched it - yummy mice in the green, green grass, I guess. How cute and innocent it looks on the photo!
Stubentiger = German for house cat

I don't know much about cats, but isn't it dangerous for the cat to wear a collar outside? Does it really make the cat less dangerous for birds with the little bell on it? Bell in large.

19:45 CEST 14,1°C