Eruptions of Old Faithful geyser
The first two data sets above show two distinct clusters, so there seem to be two different types of eruption. On seeing the clusters, a scientist would investigate what other characteristics of the eruptions are different between eruptions of the two types.
In the last two examples, the clusters are not as distinct and it is not as clear whether or not they are just random peaks and troughs. A good data detective would investigate further.
The Old Faithful is a geyser in the Yellowstone National Park in the USA that is known for its regular eruptions. Volunteers collected information about all eruptions in October 1980 (except for those from midnight to 6 am). The first data set shows the durations of these eruptions.
The second data set displays the times between successive eruptions.
The third and fourth data sets are artificially generated.