I am not going to apologies for my English this time, because last time everyone said, it is OK.
For Non - Sri Lankans,
1. Gadawila = Earth Worm
2. Rs:100/- = Considerable amount of pocket money for a child (at least those days)
Now the Story..
Grandpa (seeyaa) went out for his daily morning walk. While he was walking, he saw a gang of small lads sitting around and doing something on the muddy ground. Curious grandpa went near them and had a peep. They were playing with a Gadawila (earth worm).
Grandpa asked one lad, 'son, what you are trying to do?'
Lad said, 'we just pulled this Gadawila from this tiny hole on the ground, now we want to put him back in his house'
Grandpa, 'OK, whoever could put him back in his hole again, will get Rs:100/- reward from me'
Now the lads are trying hard, everyone had their turn, but whenever they tried, Gadawila wiggles around, struggle and moves, none of them could put him back in the hole because of his flexible body.
Suddenly one lad got a great idea, he ran to his house and came with a tin of 'wood varnish'. He opened the lid, dipped the worm in varnish, holding from one end he took Gadawila out and let him dry for a minute. Soon the Gadawila became very rigid and stiff. He brought one end near to the hole in the ground, gave a little push, this time Gadawila went in without any problems. (not sure Gadawila was alive any more)
Then the lad shouted, seeye (Grandpa) give me my Rs:100/- . But, surprisingly Grandpa did not tell a word, he just walked away. Lads went behind him and tried, but no success, grandpa just walked home ignoring the lads. You know these children, they are not greedy like us, soon they forgot the incident and started playing again.
Next day, when lads were playing, they saw this grandpa walking by. They shouted, 'Seeye Seeye (grandpa) how about that Rs:100/- you promised yesterday?'.
Without any hesitation, grandpa came and opened his purse, gave Rs:200/-.
Surprised by the reward, lads asked 'but you promised only Rs:100/-?'
Grandpa said, 'That's fine, other Rs:100/- from Grandma'

P.S.: I hope this joke wouldn't effect the Viagra sales.