That paw sticking out of the letterbox belongs to a real cat.
Some people may have missed it or mistaken it for just more junk mail.
But not Ms Nurhayati Hashim, 22, who heard an animal's cry for help when she walked past the letterboxes at Block 169, Bukit Batok West Avenue 8, around 1pm on Friday.
She pushed the slat and the cat reacted by reaching out with its paws.
With only enough space for letters to be slipped in, there was no way the cat could have crawled in.
The key for the main opening at the back of the letterboxes is held by a postman, so Ms Nurhayati went to the unit indicated on the letterbox but a woman who opened the door said she could not communicate in English.
The woman then called her daughter-in-law, who spoke to Ms Nurhayati over the phone to explain that she did not have the key to the letterbox. She said she was merely tending the flat for a tenant who was overseas.
Ms Nurhayati then called SingPost for help. A SingPost spokesman told The Sunday Times yesterday that an Inspector of Post responded immediately.
He arrived at around 1.30pm and opened the letterbox to release the black cat.
The SingPost spokesman said this was the first time an animal has been found in a letterbox.
Ms Nurhayati, who is unemployed, said: "The cat was fine when it got out. No injuries were seen."
She said residents, who had tried to help the cat while it was locked inside the letterbox, fed it after it was released.
Ms Nurhayati posted videos and pictures of her encounter on Facebook. It went viral, with more than 1,800 likes and 3,400 shares.
Cat Welfare Society (CWS) executive director Laura Ann Meranda said CWS will be working with the authorities to verify, by retrieving closed-circuit television footage, "if there was any deliberate intention to harm the cat".
"We appreciate the quick action of the resident and the SingPost officer who acted promptly to help the cat," she said.