Why are we ticklish?

Light touches, by feathers, spiders, insects or other
humans, can stimulate fine nerve-endings in the skin
which send impulses to the somatosensory cortex in the
brain. Certain areas are more ticklish – such as the feet –
which may indicate that it is a defence mechanism
against unexpected predators. It is the unexpected
nature of this stimulus that means you can be tickled.
Although you can give yourself goosebumps through
light tickling, you can’t make yourself laugh.