It comes from a post on hyperboleandahalf.blogspot.com called "Dogs Don't Understand Basic Concepts Like Moving."
You should read it. It is written and illustrated by the talented Allie Brosh. Erika's blog artwork sometimes reminds me of Allie's work.
Quick warning: this post is free of profanity, but some of the other posts on Hyperbole and a Half are not. You might find them worth reading, but don't say I didn't warn you!