Why?

A while later, Aru stepped into the newly constructed medicine hall. 

A medicine hall was analogous to a modern-day hospital. Once the tribe grew, it was impossible to treat everyone personally. So, many people were trained in medicine and a medicine hall was created to house and treat the injured.

This time, Aru walked in with a clear purpose in his mind.

'Beating up Kaan again will get me two bison legs. Preventing him from becoming the chief gets me ten more. Convincing the leaders will get me another ten bison legs and an entire mud pig. In total, there will be twenty-two bison legs and a mud pig. It's worth it.' Aru said to himself.

Initially, Nom and others thought Aru needed ten bison legs and a mud pig to do everything. So, they excitedly agreed to his demand. But later, they realised he was asking for a separate fee for all three tasks. 

They felt a little pang in their heart, thinking about procuring all that.