For two days, she thought the foul smell lingering at the corridor outside her flat came from a pile of rubbish.
But on Thursday afternoon, the stench became much stronger and it seemed to come from her neighbour's flat.
"It smelled like blood that had been left in the open for a couple of days," said Madam Sharifah Noor.
The 64-year-old, who lives on the third storey of Block 641, Ang Mo Kio Avenue 4, went to check on her neighbour, Madam Zubaidah, who lived alone one unit away from her.
She was joined by a few other neighbours who were also concerned about the 74-year-old woman.
When Madam Zubaidah did not answer them, they suspected something was wrong.
Madam Sharifah, who regularly visited her, said: "The gate was locked, but the door wasn't, and her shoes were inside the flat, so we knew she was at home."
Madam Sharifah's husband quickly called the police.
Their worst fears were confirmed when paramedics arrived, forced the door open and pronounced Madam Zubaidah dead.
"They told us that she had been dead for about three days and there was blood on the bed," said Madam Sharifah.
She added that Madam Zubaidah had high blood pressure and a blood clot in her leg that caused it to swell.
Indeed, the swelling was so bad that she was shuffling when she walked, Madam Sharifah said.
Madam Zubaidah had lived in her flat for about 12 years. Two years ago, she started living alone after her son was sentenced to seven years' jail.
Her two-year-old grandson has been under the care of Madam Sharifah since then.
Madam Zubaidah was a familiar face on the third storey and Madam Sharifah described her as a friendly person.
"We used to go marketing together and hang out below our flat to have coffee and kueh. She was a nice person to talk to."