Maybe your pulse quickens, perspiration starts, or you flush for no apparent reason whatsoever.
Your body's reaction seems to be completely out of your hands.
An Aries' ability to contain their feelings is a strength they rely on when they're infatuated. They ignore their fears and take calculated risks instead. From time to time, it turns out that way.
If a Taurus has a romantic interest, they won't tell anyone. Nobody can understand why Taurus is second-guessing themselves or why they feel bad about a joke that didn't land.
In the midst of a crush, Gemini's emotions can swing wildly. Despite their best efforts, Gemini's emotions get the better of them, and the sign comes on too strongly.
Cancer tells themselves that pursuing their crush is pointless and gives up on the idea altogether. Unfortunately, Cancer then gets down on themselves for being so gloomy.
Flirting is the first reaction for Leos when they have a crush. Leo needs to find a way to get into their orbit, and they will be utterly smitten with their crush. Though he keeps it subtle and light, Leo is also slightly sensitive.