Sun flowers being attacked

my sunflowers are growing really tall but the leaves seem to be attack by something. I have checked the leaves and bed and can’t find any sign of slugs or caterpillars, there are no sign of eggs or anything on the leaves, even one of the flower heads seem to have been attacked as well.
The other leaves are ok and in pretty good condition

               

Any suggestions ?

My guess would be a slug or snail. Probably only one, go out at dusk when it’s damp and you may find it.