Girls, Why does this girl keep looking or smiling to herself we don’t know each other?

I train at the gym I am a athlete (weight lifting and powerlifting) so I have build quite a big physique however naturally. My legs are quite muscular so when I wear shorts I sometimes practice a few poses to see where I could improve or what position looks good and relaxed.

I noticed some girls in the corner I and they kept looking. I don’t pay much attention, I’m there to work out. But then I saw her in the lock supermarket. And she kept looking when we passed. I was minding my own business. Didn’t look at her. But she kept looking.
then when gyms re opened again she saw me in the gym again and I often see her when I go in. But when ever I walk in the room and she’s working out she starts smiling to herself then she stops and looks all serious and in a bad mood. Why does she keep looking , and then again at the super market. Then smiling to herself when I walked in the room then just looked all serious and kept to herself.
Girls, Why does this girl keep looking or smiling to herself we don’t know each other?
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