What does it mean when a guy or girl face lights up when talking about a guy/girl?

[Anonymous]

His face lit up like a Christmas tree after saying her name.

[LiamJHayden]

He is either infatuated with her, or thinks very highly of her.

[beefcakebradybatson]

He's in LOVE !!!

[Asker]

Why does he look me up and down when I'm not looking? Someone said he was staring at me while looking at me from head to toe. And while he's talking to someone else and he sees me his eyes leaves the conversation and follow me to the point he forget what he's talking about his whole body neck included follows me until i disappeared out of his sight. He says he's observant but to what degree that being observant just observant when does it indicate that something else is happening here. I don't have much experience with guys so I don't know if this is normal male behavior or if this is something that men do for no particular reason regarding staring.

[Nikki1989]

He either really likes her or is seriously high.

[CuriousHubby]

He likes her or is crushing

[Wise4myage]

He’s into her.

[avery58]

He probably likes her

[morganherrel]

LOL why do you think?