Examing archives and spotted this – Adrian Loo and I were with some undegrads at the time, setting them up for their research work at Sungei Mandai Besar mangrove on 23 Dec 2005.
Something alerted me, so I stopped the student who was about to peer inside a bush. I walked around and there it was, an Equatorial Spitting Cobra (Naja sumatrana) inside the bush.
It glid away, disturbed to the back mangrove subsequently. And there were two.
See also “A snake came to my water-trough. On a hot, hot, day…” and Ecology Asia for notes on the species.
Otterman speaks... 
encountered one on the pavement next to the PCN bicycle rental kiosk near Changi Ferry Terminal earlier this year…many cyclists passing by thought it was a discarded inner tube & almost cycled over the poor thing before it could retreat back into the surrounding vegetation.