Fear of objects with small holes, including sponges is called "Trypophobia".
According to researchers Geoff Cole and Arnold Wilkins of the University of Essex, the brains of trypophobic individuals associate the holes with some kind of danger. The kind of danger one senses or imagines it yet to be established.
The fear of holes not only covers holes in the form of images, the individual may also fear holes in meat, clusters/pores on the skin, on vegetables or fruits or even those in sponges, wood, honeycombs etc.
Understanding trypophobia, find out why some people fear holes at FEAROF.NET.
What scares you? Take a look at the Top 20 unusual phobias compiled by BathChronicle.
Check out some Self-Help Tips for Managing Phobias from HealthCentral.