Sisters don't need words. They have perfected a language of snarls and smiles and frowns and winks - expressions of shocked surprise and incredulity and disbelief. Sniffs and snorts and gasps and sighs - that can undermine any tale you are telling.
I captured a set of photos of my my two nieces, Jesse, age 4, being the BIG sister, and Sara, age 4 months. It's a big deal being a big sister (I know, I'm one twice)