After her son played outside, microbiologist Tasha Sturm asked him to press his hand into a petri dish so she could see what colonized.
She also posted two close-ups of some funky growths.
On the left is a close-up of the organism on the palm print, which Sturm speculated is a Bacillus species, normally found in soil. On the right is an unknown organism, which was outside the imprint, so she wasn't sure if it came from her son's hand or was a contaminant.
To make a handprint yourself, Sturm included a few basic instructions in the comments (though you'll need some specialized equipment and basic safety know-how).