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It's always surreal to see media based on puppet characters that portrays them as regular people who walk around and go places on their own. While in the fiction of the puppet world they do have their own lives, there's an audience understanding that these things are being operated by a person. If it's something like The Muppets or Sesame Street where the puppeteers aren't really seen or shown, then it's not as weird, but in the case of Mortimer and Charlie, the lack of Edgar Bergen is noticeable. The ventriloquist is an integral part of the ventriloquist act, and having the dummies walk and talk without him just doesn't feel right.
On top of that, we see that in the fiction of this dummy world the dummies are actually the size of ventriloquist dummies. Had Edgar Bergen actually been in the comic, he would appear normal size, and they would appear the size that they do in his act. This allows for the punchline of today's strip, which shows Mortimer Snerd, who is small enough to fit into a baby's cradle, falling asleep in the baby furniture display. Why he has to get yelled at by a disgruntled wife in order for that to happen, I'm not sure. Having Mortimer wait in line for the phone booth forever, ask Charlie what kind of star he wants, and then go back to the store only to find it closed would work just as well. But I guess that wouldn't be Edgar Bergen-esque enough.