Compare the role of tendons in the skeletal system and the muscular system work together to a bridge between two cites.

Tendons are there to help your bones/muscles move and operate correctly and without tendons your muscles and bones would be idle.
Without a bridge between two neighboring cities, they would have to depend on themselves independently because they would not have the ability to mingle/work together to both their benefits.  

Your dog can sniff at or even eat a bit of catnip. the herb is edible and not harmful. just don't expect them to roll around like a cat would! your dog may scrutinize catnip by licking and smelling at it, or be totally indifferent to this stimulant.