The holiday period often coincides with an increase in domestic and family violence.

It's Christmas day and the rellies are gathered around the living room.

Key points: Christmas and New Year have been linked to higher rates of domestic violence

If a physical assault has occurred or safety is compromised, the police should always be the first port of call

Friends, family members and bystanders can also help support victims and safely challenge their perpetrators

The banter and beers are flowing freely, but you just can't shake the feeling something's not quite right.

It could have been the way he talked to her, or maybe it was the way he grabbed her arm.

You wonder if everything is okay at home. Maybe you should say something.

But what if you make the situation worse?

"I think friends and family and communities are still too scared to say something, because they're scared they might say something wrong," says Dr Sarah Wendt, a Professor of Social Work at Flinders University.

"People are scared they'll inflame the situation and make it more volatile."

But this doesn't have to be the case.

According to the experts, friends, family members and even bystanders can play an important role in supporting victims of domestic violence and safely challenging their perpetrators.

While women make up the overwhelming majority of domestic violence victims, men also suffer from abuse.

So how do you know when you should intervene? And if you do, what do you say?

Why does domestic violence increase over Christmas?

Seasonal changes and public holidays like Christmas and New Year have been linked to higher rates of family, domestic and sexual violence, and while there is no single explanation for the phenomenon, researchers believe factors like increased contact between victims and perpetrators, financial stress and alcohol all play a role.

During the summer months, female victims are also most likely to be hospitalised.

"When you think about what domestic and family violence is, it's about fear, control, power," Dr Wendt said.

"[For victims] there is a sense of survival I think through everyday life, but when you come up to Christmas and New Year, maybe women and children see an opportunity where, if they were going to leave, this is it.

"On the other hand it's a moment where a perpetrator can exert much more frequent use of his violence."

What are the signs to look out for?

It probably goes without saying that the most obvious sign of domestic violence is physical abuse — and the experts all agree, if you see it happening, you should call the police.

But there are other subtleties that can be harder to identify.

"Maybe that's being observant about the way he talks to her in public, maybe the way he puts her down, maybe the way she responds to him," Dr Wendt said.

Dr Heather Nancarrow, CEO of Australia's National Research Organisation for Women's Safety (ANROWS), also points to controlling behaviours.

"They're fearful of their partner and that fear can be triggered simply by the way he looks at her, or he might touch her on the shoulder," Dr Nancarrow said.

"It can be a look, it can be a gesture. There's not necessarily any physical contact or physical violence, but often those strategies of control are effective because of prior experiences of violence."

Should you intervene?

Intervention is a difficult topic to navigate, and there's no one-size-fits-all answer.

Above all, the experts advise that people read the situation before taking action.

If a physical assault has occurred, or your safety or the safety of others is compromised, the police should always be the first port of call.

In other cases where suspected abuse is not as obvious, simply offering an ear can be an effective way of stepping in.

"We all have these instincts to rescue or coach or intervene, but I think the first step is to just reflect yourself," says Professor Kelsey Hegarty, an academic general practitioner who holds the joint Chair in Family Violence Prevention at the University of Melbourne and the Royal Women's Hospital.

"You want to try and check in with them about their needs. Listen to what they say, enquire about their needs."

It's a sentiment echoed by Dr Nancarrow, who recommends creating a safe space to broach the conversation.

"One thing that they might do is to ask [the person] who's been targeted with this abusive behaviour to help them out with something in the kitchen," she said.

"Give them an opportunity to be alone where the bystander can say, 'I've noticed these behaviours and I'm worried about you. Is there something I can do to help you? Are you feeling safe'?"

What should you say to the victim?

If you have opened up the conversation with someone you believe to be at risk, the experts recommend focussing your concerns on them, rather than naming the perpetrator or their behaviour.

Some of their suggestions include:

"Hey, are you okay? I'm just feeling a bit worried about you."

"I just saw that happening, how are you feeling? Is there anything I can do?"

"You're very welcome to stay here tonight. I'm here for you, don't hesitate to ring day or night if you need help."

They also recommend finding ways to continue the conversation in a safe environment, like asking to catch up for a coffee in a few days time.

"Some victims will say, 'I don't know what you're talking about' and they'll deny it," says Dr Nancarrow.

"But if you don't judge or impose on them in any way and open the conversation, then they know they've got a trusting ally that they can go back to at another time."

Above all though, the experts caution that any conversation should be free from judgement or pressure.

"You want to signal to her that you're with her and at any point, would come and would help," says Professor Hegarty.

"But the thing is, pressuring people to leave or to do something they're not comfortable with, it puts a lot more pressure on them, and that's not what you want."

What should you say to the perpetrator?

The experts believe there are also opportunities to challenge the behaviour of perpetrators in a way that does not risk alienating them.

"We can challenge subtly and softly. It doesn't have to be, 'This is domestic violence and you're a perpetrator'," says Dr Wendt.

Some of their suggestions include:

"I'm just a bit worried about where this is leading."

"Come on mate, don't talk about your partner like that."

"I'm not sure what's going on for you, but I don't think this behaviour is okay. Tell me what's happening."

Pointing out the problem in a safe way may enable the perpetrator to step back and reflect on their actions, Dr Nancarrow says.

"It's kind of a respectful way to intervene and not humiliate, because I think that risks escalating the problem," she says.

"It's expressing genuine concern, but also firm disapproval of the action or behaviour."

What about kids?

If you have concerns about how a child is faring, the experts recommend broaching the issue through the non-offending parent.

"We know through research, when children and the non-offending parent have a bond, it's the most wonderful safeguard for children," Dr Wendt says.

"If you see that worrying behaviour, you can say, 'Hey, I'm worried about your son, is everything okay? Are you two safe?'."

Dr Nancarrow says these sorts of conversations need to be approached with care, and should be free from judgement.

Importantly, they should avoid placing pressure on the victim to leave a relationship because of other peoples' concerns for the welfare of their child.

"Don't assume a woman staying in a relationship is not protecting her children," she says.

"The safest thing for them may be to remain in the relationship.

"It's complex and what appears to be obvious to a lay person isn't obvious. Leaving a violent relationship can sometimes be the most lethal thing to do."