Clownfish "count" white stripes to determine if an invader is friend or foe

But clownfish can be quite territorial when it comes to defending their host anemone from intrusion by others, particularly those from their own species.

Mathematical ability is often considered uniquely human, but in fact, scientists have found that many animal species...seem to possess at least a rudimentary counting ability or number sense.

Read at Ars Technica