GEOFF Boycott once said of facing the world's most hostile fast bowlers: "To have some idea what it's like, stand in the outside lane of a motorway, get your mate to drive his car at you at 95mph and wait until he's 12 yards away before you decide to jump."
Presumably, blind terror will be the dominant emotion.
You can imagine it is much the same when you line up opposite the All Blacks when they are doing the haka.
Butterflies flying everywhere in the stomach, muscles tightening, mind freezing, worry about whether you did bother to put a signature on that life insurance form that came your way a couple of weeks earlier.
When you're a youngster of 21, playing your first Test against another country, the nerves must be unbearable.
Fight or flight? What's it to be?
It took just a few minutes for Liam Williams to answer those questions last week.
New Zealand swung the ball along the line and for a moment an overlap seemed to beckon.
Then a red blur flew out of the defensive line in the direction of Israel Dagg, connecting square on with the full-back at the very moment he received the ball.
Smack — Dagg was not so much knocked back as engulfed.
Cue one of the biggest cheers of the evening.
Minutes later, Corey Jane had the same treatment, then Julian Savea found himself the subject of a missile-like hit from Williams, a tackle that again drew loud appreciation from those watching.
The All Blacks discovered what all at the Scarlets had been aware of for some time, that the former scaffolder from Waunarlwydd doesn't do fear.
If you had to hazard a guess where he lives, you would probably come up with Harm's Way, so much time does he spend there.
The Daily Mail said the 6f 2in, 13st 6lb was "built like a Twiglet with the power of a tornado".
On Twitter, Williams styles himself as a "professional bomb defuser with the Scarlets". He certainly has the nerve.
Not that he would acclaim himself for playing with such courage against the All Blacks. To him, it was all in a day's work.
"You can't allow yourself to get intimidated on the pitch," he said after being selected on the wing against Australia.
"Making tackles is just my game. I tried to go out there and do exactly as I do for the Scarlets.
"I was a bit nervous at the start, but once you get into it you realise it's just a game.
"It was good to make a tackle early on. Dagg is class — it was good to be up against such a top player — but the chance was there to take man and ball and fortunately for me I got it right."
Williams may be a few pounds lighter than your average Test player, but he claims he is in the shape of his life and there is a picture on his Twitter account to prove it.
If it is a body double at the side of a swimming pool, the chap in question clearly has kept his gym membership up to date.
"I guess the journalist who had a bit of fun in the paper is right in some ways," said Williams.
"I am 86kg and 6ft 2in, but in a game I have no respect for my body. I just put it on the line for the team. That's what I did against the All Blacks. I stick my body on the line. If I get hurt, so be it.
"Is tackling a state of mind? You just need a bit of guts and a bit of heart. I think I have both of those. I put my head down and if I pick up a bump that's the way it goes.
"You just have to go for it. If you go in half-heartedly, you will come out second best and you are more likely to get hurt."
One area of his game that Williams hopes to improve against Australia on Saturday is under the high ball.
Usually so safe for the Scarlets, for whom he plays full-back, he dropped three against New Zealand, often coming from too deep to take them.
"I've seen on the laptop this week that I was too deep to start with. It's all about coming up a couple of yards closer to give me more chance of taking the ball, rather than jumping from far away. The idea is to get directly underneath the kick. That makes it much easier to take them," he continued.
"If Australia put the ball in the air for me this week, I'm sure I'll go up and catch them."
Williams will face Nick Cummins this week, the powerful wing who caused England so many problems at Twickenham.
"He's a good, strong winger, but if he comes down the channel I'll just have to chop his legs," said Williams.
"I don't care whether an opposition wing is powerful or small and nippy. It doesn't really bother me at all. If he's big, if he's quick, if he's hard — it's all part of the game.
"You just have to throw yourself into it."
Did he believe Cummins might have picked up on the Twiglet comment? "He might have," said Williams. "He might think: 'He's 86kg and I'm going to run over the top of him'. If that's what he thinks, happy days."
Williams garnished a number of his big tackles against the All Blacks by shoving the unlucky recipients hard in the chest.
He is in the side again this week as George North continues to be sidelined by injury.
It is an opportunity Williams aims to make the most of.
"You just have to do your best," he said.
"It's a hard back three to break into.
"We have probably the two biggest wingers in world rugby and Pens (Leigh Halfpenny) at the back is rock solid, kicks all his goals and doesn't do anything wrong. But with George being injured it's a chance for me to go out there and have a go.
"I don't think I need to put on weight, but if people want me to I'll go with it.
"I'm not the best in the gym, but I'm certainly not the worst. I guess you'd call me wiry strong. George is huge, 17st and really powerful. I'm skinny and wiry."
Williams hopes Wales can round off their series on a high note. "We definitely need a win," he added.
"The autumn hasn't gone too well with the three losses.
"But I think we owe them a win after losing 3-0 in Oz.
"Hopefully, this weekend will be the time for it."