My dog rolling in grass

My dog flips over on her back and rolls around in the grass when we go for a walk. Look at the photos below. Hilarious, aren't they? Are you maybe curious why do dogs actually do this? I was curious myself and I have just checked it Wiki Answers; dogs roll over because of their instict
Wolves, in the wild, would roll around in the grass - or poop of the animal or creature they are hunting - to partially cover their scent, making it easier for them to approach the prey that they are after, and for them to get closer to them or it before it or them notices (...)Another logical answer would be because it feels good. The good green grass is usually, for the most part, cool and slick. Another concluding answer is because they are expressing their joy, happiness, and playfulness.
Yes, the truth is that our furry friends don't need to catch their prey, but the blood of their ancestors - wolves is still flowing in their veins. My dog always looks happy when rolling on her back, I don't mind her doing this, as long as the grass looks clean and well-trimmed .... and of this I can be sure only in my own garden :-)