From examples I found, it’s not usually that periodic, but some mantis species make a very scratchy sound when threatened, sometimes repeatedly, but at more irregular intervals.

My yard is full of praying mantises, but they are usually dead quiet, I’ve never heard one make a noise (I try not to bother them). It’s definitely not a common trope sound like crickets… I was hoping there was some nature documentary that aired in the early 80s that featured a mantis sound that Larson might have seen, that could have inspired this cartoon idea, but so far can’t find a specific one. There was an episode of Life on Earth from 1979 (presented by David Attenborough of course) about insects that featured some mantis stuff, and lots of insect sounds in the background, but not a specific mantis sound (they seem to play a cricket sound during the mantis scene in the background)

There was also a song “Praying Mantis” released in 1985 by Don Dixon that featured praying mantises in the video, but can’t connect that one of the strip either :)

I suppose it’s also possible that is supposed to be a cricket rather than a mantis… or that Larson didn’t really differentiate between them or their sounds, and it might have been as broad as “insect interested in insect sounds”

Edit: I had an alternate thought - maybe the mantis wants to eat a cricket ! :) But then the connection to his master’s voice is weakened… oh well, dissecting jokes really does kill them…

Praying mantises make sounds that sound a lot like a record scratch.

The water heaters are usually gas here though, so electric system doesn’t really matter. Tankless heaters have become a lot more common over past decade or two, both gas and electric. For electric ones you just use a 240V circuit. Most electric appliances that need a lot of power run on 240V here, 30A and even 50A or 60A circuits are common and provide enough power for household needs.

I live in the US and every dishwasher I ever owned had a heating element, and was capable of heating its own water as needed, depending on what cycle was selected.

Same with my washing machines, my current one even has a steam cycle.

I feel like if dishwashers without heating elements were ever a common thing here, it must have been many decades ago.

It’s a Bell 548A jack to be more precise. It’s compatible with both 283B (the older square shape) and 505A (the later round shape) plugs