A black and white dog is drooling whilst walking on the grass.
A dog is urinating on the grass as it goes for a walk.
The phrase "whilst walking" denotes that the dog is in the action of walking while it is drooling at the same time. The phrase "as it goes for a walk" implies that the dog may not be in the actual action of walking, but only preparing to walk. Therefore, the dog may in fact be standing still while it is urinating.
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