The best birthday surprise I get is from the neighbor's dog while her husband isn't home.
Scenario: The main character, a vulnerable housewife named Sarah, is celebrating her birthday alone at home. She's bored and a bit sad until she hears rustling outside her window. Looking out, she sees the neighbor's dog, a massive German Shepherd with an imposing presence. The dog begins to mount her, causing the skirt she's wearing to ride up and expose her pale legs. As the beast continues its assault, Sarah's heart races in fear and excitement.
Action: The dog's rough tongue licks her neck and ears while its thick member presses against her panty-clad pussy. She tries to push it away but finds herself aroused by the taboo act. The neighbor's dog senses her arousal and becomes more aggressive in its advances.