A complete guide to modular holds - hold shape
The size and shape of a climbing hold is a major part of the climbing experience. The hold surface can be rock-like irregular (fractal) like the shapes below.
These irregular shapes (plastic and real rock holds) require the fingers to be more "novel" in how they get to use the hold. The holds are shaped "wierd" from an everyday use perspective. Shapes very unlike the broom handles, drinking glasses, steering wheels and all those comfortable but unnatural objects we grab a hold of each day. The irregular rock-like shapes tend to offer more grip so they make good choices for walls at camps and schools where beginners have their first climbing experience. Realistic holds are also nice if you don't have access to outdoor climbing (say Florida) and your wall is your total climbing experience.