Crows can count... out loud! They do so similarly to human toddlers who are learning to tally things up. A neuroscientist trained birds to produce a number of calls in response to random visual cues.

Most of us have little trouble working out how many milliliters are in 2.4 liters of water (it's 2,400). But the same can't be said when we're asked how many minutes are in 2.4 hours (it's 144).