Cow on the Track

A passenger train is creeping along slowly. Finally it creaks to a
halt. A passenger sees the conductor walking by outside.

"What's going on?" she yells out the window.

"Cow on the track." replies the conductor.

A few minutes later the train starts up, moving along slowly. Five
minutes later it stops again. The woman sees the conductor walk by.

"What happened?" she yells out the window. "Did we catch up with the cow
again?"