It really was amazing to watch it - you could see his mouth working and the lettuce leaf actually disappearing whilst you watched! Now slugs are one of the only things that make my skin really crawl but it was incredible to watch.
I don't really mind them and I know I was fascinated by them as a child and so too are my little girls. They find it very funny when they crawl all over their hands and arms. When I looked at this pot there were 10 caterpillars on it and they had decimated the nasturtium but hadn't touched the geranium.
Also note the black dots around the base of the pot - caterpillar poo!