A man boarded a bus using a snake as a face covering.
The commuter and his reptilian mask, which was wrapped around his neck and mouth, were seen on a bus from Swinton to Manchester on Monday.
One passenger, said she thought the passenger was wearing a "funky mask" until she spotted it slithering over hand rails.
Transport bosses in Greater Manchester confirmed a snake was not a valid face covering.
The eyewitness, who asked to remain anonymous, said she found the incident "really funny", adding the animal did not seem to be bothering any of her fellow passengers.
She said: "No-one batted an eyelid."
Using a face covering on public transport is mandatory, except for children under the age of 11 or those who are exempt for health or disability reasons.
A Transport for Greater Manchester spokesperson said: "Government guidance clearly states that this needn't be a surgical mask, and that passengers can make their own or wear something suitable, such as a scarf or bandana.
"While there is a small degree of interpretation that can be applied to this, we do not believe it extends to the use of snakeskin - especially when still attached to the snake."