I suppose they're referencing a popular video game mechanic, in which skill-building works by collecting skills in a limited number of "slots". The claim is th

I suppose they're referencing a popular video game mechanic, in which skill-building works by collecting skills in a limited number of "slots". The claim is that while humans may be able to master a large number of different skills, few of them are limited to humans in and of themselves (and not available to some other animals as well).