How can you tell when a guy admires your body?

I've always gotten compliments from guys on my body. There's this guy who is really cute and I always see him leaning in from his desk when he sees me and follow me with his eyes wherever I walk to. He does it with a normal expression and does it quite a lot. He makes it be known that he's staring too. Why would you think he'll make it "known"?
How can you tell when a guy admires your body?
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