What is the spark?

What is the spark?  What is connection?  What is clicking with someone?
The spark is wanting to write back to them before they've even written back to you.
The spark is being excited to see them come online.
The spark is finding even their so-so jokes and random comments really funny.
The spark is having intrusive thoughts about them all day (and night).
The spark is wanting to 'like' almost all of their Facebook posts.
The spark is realizing you get a silly little grin on your face whenever you think about them.
The spark is feeling happily anxious about the possibility of seeing them.
The spark is getting a tingle through your body when you spot them across the room.
The spark is not wanting the time to end when you're together.
The spark is fantasizing about future get-togethers.
The spark is fitting your schedule around them, rather than fitting them into your schedule.
The spark is feeling comfortable with them, like you've know each other forever.
The spark is sharing parts of yourself you normally keep hidden.
The spark is knowing that even from day one, you would help them out of any jam.
The spark is being at home in their arms.
The spark is having a list of reasons why it wouldn't work, but still wanting to be with them.
The spark is wanting them to be happy, even if that means being happy with someone else.