The how-to-survive-terrorism-for-dummies class is being held at Israeli Defence Forces gym in Caulfield and it's almost full today. Israeli Defence Forces films play on loop in the background. So overwhelming has been the demand for the course, gym founder Avi Yemeni plans to take the concept nationwide. Mr Yemeni is the estranged brother of Manny Waks, who blew the whistle on child sexual abuse in Melbourne's Orthodox Jewish community.

"Some people will take action", Mr Offenbach tells his audience, who today number about 70.

"Some people will stand and watch. Being a bystander is more dangerous than being somebody who takes action - or somebody who runs away."

A former Israeli Defence Forces soldier and policeman, Mr Offenbach has a thick neck, shaved head and a chest that looks like a cliff-face. He travels the world running these courses.

Most of his participants today are in gym gear, but Dona Miriam Mendez da Costa has come dressed in white for Jewish Orthodox services.

If there is a terrorist attack, she thinks it's most likely they'll target her service – just as they targeted a kosher food supermarket in France. So she wants to be prepared, she says.

Meanwhile, Mr Offenbach has lined his participants against the four walls of the gym. They are instructed to get down on their bellies and move with as much pace and silence as possible.

Getting low is very important, he says. "Bring your tushy up, you'll get a bullet in your tushy".

The people slither towards each other, massing in the centre of room. Some dodge, some simply go over other participants – and it's here that our first casualty occurs, apparently caught under another slitherer and trampled.

She – screaming in pain – cannot be moved from where she falls. After checking on her welfare, and calling an ambulance, Mr Offenbach moves his participants away from her and carries on with the training.

She won't be the only one. By the end of the session, two people are sitting out with back injuries and another man has dislocated his toe. The intensity is high.

A well-stocked arsenal of blue plastic machine guns hang on the wall. They won't be used – Mr Offenbach is keen to ensure nobody attending thinks they have the skills to take down an armed offender.

Avoidance is always the best strategy and the key is situational awareness.

"Be a little bit aware of your surroundings. A little bit of awareness will make sure that if you're sitting in your favourite cafe and somebody comes inside who doesn't fit,"  Mr Offenbach snaps his fingers. "Ping".

"You cannot carry a submachine gun without people noticing. If you're oblivious to your surroundings, yes. You don't need to be James Bond."

If worst does come to worst, physical aggression can be used. Get close to the terrorist – pretending to cry usually works well, Mr Offenbach says – and then dive on their legs to trip them up.

For that to work, "you need to be a little bit crazy", he says.

"And with a little bit of God on your side".