Who is your wife seeing?

Three friends - Bob, Joe and Mark are having beer at their regular watering hole.

Bob says to his friends, "I found plumbing tools in my wife's wardrobe. I think she is seeing a plumber."

Joe says, "I found a first-aid box in my wife's wardrobe. I think she is seeing a doctor."

Mark adds, "Wait till you hear what I have to say. I found a cowboy hiding in my wife's wardrobe. I think she is seeing a horse!"