If you want to know if Spot loves you so, it's in his tail
When dogs feel fundamentally positive about something or someone, their tails wag more to the right side of their rumps. When they have negative feelings, their tail wagging is biased to the left.
It suggests that the muscles in the right side of the tail reflect positive emotions while the muscles in the left side express negative ones.
Sounds like a good candidate for an Ig Nobel prize.