Found a simple solution which doesn't involve loads of javascript...
<details><summary><b>Click here for explanation</b></summary>
It looks as though there is a increasing, but curved, relationship between brain mass and body mass but the plot is very hard to interpret because almost all of the data are very close to the origin. This is because both brain mass and body mass are strongly positively skewed: here's a histogram of body mass to make the point.
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