Whether they are a man or a woman, the best way to find out if the object of your crush returns your affections is probably just to talk to them.
But in judging whether there's a spark between you, what they are saying may not be as important as how they say it.
Dr Marina Kalashnikova, a speech and language researcher at the University of Western Sydney, said research had shown people's voices "carry a lot of information" about their feelings towards the person they're conversing with.
And like the butterflies in your stomach, try as you might you are probably not going to be able to do anything about it.
"The information that is carried in the voice is not controlled by our conscious thinking or our intentions," Dr Kalashnikova told ABC Radio Melbourne's Lindy Burns.
It's in their pitch (that's where it is)
She said people with positive feelings towards each other began to display a phenomenon called phonetic convergence.
"The voices of the two people who are speaking to each other, if they are attracted to each other or if they experience positive emotions towards each other, they start becoming more similar," she said.
A person will change the way they speak to more closely mimic the other person.
"Changes in the pitch of our voice or in the rate of our speech, so how fast we're speaking, are happening according to how we feel about the conversation but without our conscious control," she said.
She said in some instances people even changed the content of their speech to mimic the person they're attracted to.
"We would use more similar expressions, for example, to sound more alike."
Phonetic convergence can take months to become apparent, but not always.
"This can happen very quickly, over the course of a single conversation," Dr Kalashnikova said.
"We will start slowly converging and sounding more similar as the conversation progresses."
But it's probably best not to worry too much about examining your love interest's speech patterns.
"We can interpret this information unconsciously," Dr Kalashnikova said.
She said a person's gender did not seem to affect the phenomenon, as rates of phonetic convergence had been shown to be "very similar across the sexes".
But it's not just love interests that cause us to change the way we speak.
"For example, when we speak to babies we speak more high-pitched," Dr Kalashnikova said.
And people's unconscious reactions were the opposite when confronted with someone they disliked.
"When we do not like somebody ... we will preserve our very individual way of speaking."
Dr Kalashnikova and her colleague Heather Kember wrote about phonetic convergence recently for The Conversation.