The environment?

I have *no* idea what the artist could *possibly* be hinting at...

http://www.docrat.com.au/comic/fleas-explain-1/
http://www.docrat.com.au/comic/fleas-explain-2/
http://www.docrat.com.au/comic/fleas-explain-3/
http://www.docrat.com.au/comic/fleas-explain-4/
http://www.docrat.com.au/comic/fleas-explain-5/