Keen observers of Saturday night's clash between the Brisbane Broncos and the Newcastle Knights may have noticed something a little strange.

In the dressing room pre-match, a number of Brisbane players were seen approaching a trainer for a mysterious substance he was distributing in a cup, which they dipped their fingers in to before rubbing it on the side of their mouths, making them dry retch.

The mystery substance can be revealed as peppermint oil, which is used to open up the airways of players to help them breathe better.

Broncos prop Josh McGuire is twice seen rubbing the substance into his mouth and both times it makes him gag.

Scroll down for video

Brisbane Bronco players have been seen rubbing a mysterious substance into their side of their mouths which made them gag in the sheds before the game against the Knights on Saturday

Giant winger Corey Oates is another who has a gagging reaction when he rubs the oil on the side of his mouth.

But the bad taste certainly didn't hurt the player's performance, with the team completely outclassing the Newcastle Knights 53-0 at Suncorp Stadium.

Oates scored a hat trick in another impressive display, his early season form, leading calls from some of rugby leagues greats to be a surprise inclusion in Queensland's Origin team.

At one point during the footage it seems as if the trainer takes a step back to get out of the line of fire of a dry reaching McGuire.

Brisbane players were seen approaching a trainer for a mysterious substance then rubbing it along the side wall of their mouth, this in turn forced the broncos players to gag

Broncos prop Josh McGuire is twice seen rubbing the substance into his mouth and both times it makes him gag.

Winger Corey Oates is another who has a gagging reaction to the mysterious substance.

The strange footage had some viewers scratching their heads wondering what the Broncos were doing.

The strange footage had some viewers scratching their heads wondering what the Broncos were doing.

A supporter took to Twitter asking 'What's with the Bronco's forward trying to gag themselves pre-game.'

Another asked what the substance was.

'What was that the Broncos players were repeatedly rubbing on the back of their tongues till it made them gag?'

Peppermint oil, if ingested in large quantities can cause an overdose leading to a comatose state and shock.

The Broncos face the under siege South Sydney Rabbitohs in their round eight clash in Brisbane on Friday.