Assume this species is naturally born and has evolved to not have arms. The members of the species are extremely capable of performing tasks like opening doors with their feet and mouth. Also, this species lives on a planet extremely similar to Earth, and have built a civilization almost exactly the same as ours. However, while human children (and some adults) use arm wrestling as a playful test of strength, our unnamed species unfortunately has no hands. Keeping in mind that they can accomplish most basic tasks with their feet (and sometimes the assistance of their mouth), what type of activity could serve as a suitable replacement to arm wrestling?