Caught Red-Handed

I had a hilarious experience with one of my kindy kids yesterday.
I have a system in my classroom where, if the kids do well they get a star on the board and for every three stars they get a sticker on a wallchart thingy and for every 20 stickers they get a prize.
It's been going for a month now and my top students have just started getting their first prize, they absolutely love it and are constantly counting there stickers and working out how many more they need.
I came in after lunch and my Korean counterpart tells me Roger has got 21stickers and needs his prize.
However I had remember counting about 18 the day before for him and he hadn't got anymore from me, or from her.
And also none of the kids would have got to 21 before realizing they had got 20.
So after a couple of minutes of umm what do we do, I confronted him, a 5 year old boisterous little boy, whose answer to Brad teacher's question "Did you take stickers out of my drawer and put them on the chart was a completely uncharacteristic complete silence, he looked like he was going to wet himself.
Eventually after my counterpart had to ask him in Korean, we got hm to take 3 stickers off.
It was hilarious... for me.
I'm actually surprised it hasn't happened more often, actually it probably has, just not so conspicuously.
Nice Try