The aerodynamic flow that we have on the auto.
It was followed by this exchange between Vettel and Ricciardo that highlighted the spirited mood most drivers are in before the start of the season.
The first practice was held in cool, clear conditions with the temperature reaching 21 Celsius and it was only marginally warner for the second practice.
But in the second session, when teams started to stretch their legs a little, the best Ferrari could do was fifth with Vettel, almost nine-tenths of a second behind Hamilton.
It was a positive day for those anticipating another season of close battles in the midfield, with just a single second separating all drivers bar the leading Mercedes pair and quartet anchored to the bottom of the timesheet.
Alarm bells were ringing when team engineers could be seen taking a hammer to Ricciardo's seat in the garage in a desperate bid to get the belt to fit.
"It's not doing exactly what I like here and there so that's why I'm lacking confidence".
"Maybe everyone else was struggling and then we can turn it around, but they looked very strong and much stronger than they claimed before the weekend".
With the cars not out on the track until tomorrow, Ricciardo joined drivers on the Melbourne Walk where they arrive at the back of the pits and spend time signing autographs and posing for pictures with fans.
16,277 - Red Bull will race in Australia with their youngest two drivers ever in a single F1 grand prix (Max Verstappen and Pierre Gasly - 16,277 days combined).
"Mercedes only really pushed it at the end of the test so we will only have the answers in qualifying", he said.
Home hope Daniel Ricciardo had an underwhelming debut with Renault, clocking only the 17th fastest time.
"It is a hard period but we have to make sure we are doing everything we can in the current situation", he said.
"As far as I'm concerned that's its permanent spot", he said.
There is a feeling, though, that this could be the year the tide turns.
Where Hamilton's partnership with retired 2016 champion Nico Rosberg was fraught with tension, the 34-year-old has enjoyed a much smoother ride with Bottas, who has not proved as competitive as his German predecessor. He later spun off track several times in the second.
"The auto felt better than it did at testing", said Bottas.