The Phone Call

A woman was at home alone one day,
The phone rang, she picked it up and said "Hello?" 
The voice on the phone answered "I'm the Viper I'm coming up the stairs I'm on the last step."
She was a little worried, but she shrugged it off and convinced herself it was just a prank call.
About 10 minutes later the phone rang again.
She picked it up and said "Hello?" the voice answered, "I'm the Viper I'm at the middle of the staircase."
She started thinking maybe this isn't a prank call and started to get really scared.
10 minutes later the phone rang yet a again.
The voice said "I'm the Viper I'm at your door."
She was about to dial the police when the door opened.
A short kind looking man stood at the door and said "I'm the Viper, I've come to vash your vindows."