A few days ago I had my first muggle encounter. We were at a park and I was poking here and there with a walking stick, near a stream. I heard a small voice call out "Are you a biologist?" I look up, and there's a little boy (3 or 4 years old?) walking nearby with his mother. My reply was honest: "No, I just love nature!" The little boy gave a huge grin and said proudly, "I love nature too!" The mother and I traded smiles and then some silent laughter.
I briefly considered saying what was really happening, but figured the mom might not be pleased if her son wanted to help out some strangers with a treasure hunt.