Scent of a Cat
The road in front of our house is lined with hydrangeas. Tara doesn't go near any of them but one and he always stops and sniffs at the same spot on the same branch every time! I figure it's the cat message center. He can tell by sniffing which cats have been here, how long ago and which way they were going! They might even leave more complicated messages like "Cleo got hit by a car but he's OK!" or "Ginger was spayed yesterday, send flowers!"