I, like probably most cyclists, have a healthy anxiety/respect/fear for dogs that are allowed to run loose (with very rare and notable exceptions).
On one of my local loops, though, there’s a dog who I consider an old friend. For 5 or 6 years now we’ve played this little game:
As I’m approaching his yard, if I don’t see him lurking about, I’ll call to him as I begin to wind up my sprint (I call him “Fritz” or “Der Doggie Dog”, he’s a German Shepherd). He then carefully judges his speed and angle, charges down the hill to the fence and arrives at the corner of the fence, exactly when I do, at full speed. He then rounds the corner and we race down the fence. This is a house out in the country, so it’s at least a 150 yard dog vs. bike dash. As I ride away (sometimes victorious, sometimes not), he always runs to a good vantage point along the side fence and gives me a few barks. I’ve always taken these as meaning, “good race” and “see you next time”. I haven’t seen him (or his younger protégé) in quite some time. I miss my sprinting partners/buddies.