Brain and body weight
This is an example of an outlier that is not an unusual measurement for either of the variables on their own but is an unusual combination of values. Click on crosses to identify the animals.
You might also mention that four primates have relatively large brain weights in relation to their body weights.
The business version of this page contains an example with a different kind of outlier.
This example shows the brain and body weights of a collection of animals. They are all mammals except for one dinosaur.
Since body weight ranges from 0.023 kg (mouse) to 9,400 kg (triceratops) and has an extremely skew distribution, the diagram plots log brain weight against log body weight.