After a first woodpecker had abandoned the tree hole, the second one flew up to the tree and inspected the large hole before reversing itself into the hole and disappearing into it. Judging from the splashes, it was having a bath in the water collected in the tree hole. The water could not have been very clean as the bird's feathers looked grimy when it finally came out at about the 3.45 mark.
From a conversation with a friend who is a more experienced birdwatcher, it seems that the cackling had come from a Common Flameback Woodpecker (a.k.a Common Goldenback).
The bathing woodpecker (Banded Woodpecker) saw fit to momentarily stop its bath and looked around to see what the fuss was about. Then, rather nonchalantly, it resumed its bath. The entire bath took about 4 minutes.
Time : 11.15am, 15 Jan 2012
Place : Bukit Brown Cemetary, the tree at the red-turbaned guarded tomb.
find out more about the banded woodpecker :
http://en.wikipedia.org/wiki/Banded_Woodpecker
http://www.besgroup.org/?s=banded+woodpecker&x=0&y=0
and read about Bukit Brown :
http://bukitbrown.org/
http://wildsingaporenews.blogspot.com/2011/10/bukit-brown-hope-springs-eternal.html
http://www.straitstimes.com/BreakingNews/Singapore/Story/STIStory_736000.html