Transport authorities are investigating whether hundreds of millipedes on the tracks may have caused a minor crash between two trains in a Perth suburb.
A stationary train carrying passengers was shunted by an empty train at Clarkson, north of Perth, early on Tuesday, leaving several people complaining of sore necks.
At least two were taken to hospital as a precautionary measure.
A spokeswoman from the Perth Transport Authority (PTA) said the invertebrates, which were spotted in their hundreds on the tracks, would be investigated as a possible cause.
"It is one possible cause among many - but it is very unusual," the spokeswoman said.
Drivers had previously been warned about the bizarre occurrence, with an infestation of Portuguese millipedes thought to have caused train tracks to become slippery when crushed by the wheels of a passing train last year.
The problem was reported in Rockingham and Kwinana, and on the freight network, with the PTA spraying insecticide in and around the tracks last September.
In 2009, a plague of the millipedes - latin name Ommatoiulus moreletii - overran railway tracks at Tallarook in central Victoria, causing several trains to be cancelled.