Bibliography (4):

1. Précis of How Children Learn the Meanings of Words

2. Why Some Animals Can Tell More From Less: Researchers find that densely packed neurons play an outsize role in quantitative skill—calling into question old assumptions about evolution

3. Mental Accounting in Childhood

4. Crows Perform Yet Another Skill Once Thought Distinctively Human: Scientists demonstrate that crows are capable of recursion—a key feature in grammar. Not everyone is convinced