Australia's top order collapses, Alex Carey makes the most of an astonishing, physics-defying reprieve, and a protest briefly interrupted play on day two at a steamy, humid Gabba.

The Test is tremendously evenly poised, with the Windies taking a 35-run lead into the third day after a bold declaration from the Australian skipper Pat Cummins.

Here's the five quick hits from an eventful day two of the Gabba Test.

1. Australia Day protests

Cricket Australia has taken a pretty low key approach towards this match falling on Australia Day.

No official branding has presented this Test as being an Australia Day match and, when asked about it, players such as Pat Cummins and Steve Smith have backed a change to the current date.

However, that didn't stop there from being protests.

Around two hours before play started a group of protesters entered the empty stadium and shouted slogans, forcing media off the playing surface and a brief lockdown to be enforced.

That issue was dealt with quickly, but a more noticeable protest came at the end of the first over of the day, when a man ran onto the field with an Indigenous flag, laying down on the outfield.

The crowd booed the brief interruption as security swarmed from all corners to remove the protester in quick time.

2. The half hour of hell before dinner

You know what it's like on a public holiday.

You're out playing in the street, you can smell dinner being cooked and you're just waiting for one of your parents to call you inside.

Perhaps that's what the Aussies were thinking in a madcap 30 minutes before dinner at the Gabba.

With the humidity so high it was almost visible and the floodlights boring down through the gloom, the wheels fell off remarkably quickly for the hosts.

Steve Smith, his opening credentials very much still in doubt, looked jittery and jumpy and was trapped LBW despite leaping several inches towards point to go for 6, Marnus Labuschagne was caught by a screamer for 3, Cameron Green gave away his wicket with a scoop to the skipper for 8 and then Travis Head got a golden duck, edging behind.

The Aussies trudged off for a feed — and maybe a telling off.

3. What a debut for Kevin Sinclair

Debutants have had a pretty decent summer in Australia this year.

First there was Aamir Jamal's 6-111 in Perth, then the West Indies saw Shamar Joseph take 5-94 with the ball and hit his highest first class score of 36.

In Brisbane, it was Kevin Sinclair's turn.

A beautifully constructed half century, which he reached with a huge six off Nathan Lyon saw the Guyanese all rounder pumping his fists.

And his miraculous catch at fourth slip to get rid of Marnus Labuschagne had him sprinting to cover point in ecstasy.

Given Sinclair has made his name in limited overs cricket by celebrating a wicket with a backflip, his celebrations for his first two major impacts in Test cricket were somewhat understated.

He's have probably wanted the ball thrown to him as soon as possible with that start under his belt.

Unfortunately though, his first spell with the ball did not quite go to plan, conceding 0-30 in his three overs.

He did get his wicket in the end though, and treated the crowd to a ripping backflip that had the whole stadium on its feet, ending with figures of 1-53 from eight overs.

4. The mystery of the spinning bail

It's not often that you describe the bail spinning and not follow it up with the batter's terminal statistics.

And yet that's exactly what happened to Shamar Joseph soon after dinner.

The Guyanese bowler was initially celebrating when the ball passed the outside edge of Alex Carey's bat with a tell-tale clicking sound.

Yet the West Indies bowler almost immediately pointed at the stumps, suggesting that was what the ball hit.

And he was right.

The ball clipped — with significant force — the top of the bail and sent it spinning in its groove, an astonishing feat of physics.

Would that have happened with regulation bails as opposed to the fancy light-up ones currently in use?

Who knows.

But Carey was left thankful that he was not, in fact, bowled for eight, and made the most of his second life, driving three consecutive fours off Joseph's subsequent over and passing fifty not long afterwards.

5. A deficit declaration

It's not the most unusual thing, but it's rare for any team to willingly surrender a first innings lead in a Test match.