Nice doggy

This guy drives a delivery van and he starts going out with a really rich girl. Eventually she says.
“Come round to afternoon tea and meet my parents”
So he drives his van up the long drive and parks in front of the mansion. His girlfriend meets him at the door and takes him into the huge, huge lounge to have afternoon tea with her parents. Soon he is sat on this vast settee balancing a cup of tea and a plate of biscuits trying desperately to think of something to say.
There before them, stretched out on the rug in front of the fire, is an enormous male Great Dane fast asleep. Suddenly the dog wakes up and starts vigorously licking its balls.
Still desperate for something to say the guy gives nervous laugh and says,
“I wish I could do that”
The girl’s mother replies, in cut glass tones.

“If you give him a biscuit, I’m sure he will let you”