Question

ruminants and human s both secrete hydrochloric acid and pepsin then why can't we eat grass

Answer 1

its because there r  problem with grass diet . humans stomach have difficult digesting raw leaves and  grasses . but in animals such as cows they have 4 chambers of acid to digest grass thats  the first reason . 

Answer 2

this is because as grass contains cellulose, which ruminants can easily digested where as Hans cannot because that don't have those to digest cellulose