[blacksqr]

When I was young in the pre-Slack era when you actually had to find a colleague physically to explain the problem to, this was called "cardboard engineer syndrome"; i.e., talking to a cardboard cutout of a colleague would have been just as effective.

[ThunderSizzle]

I know this as rubber ducking. Explain your problem to a "rubber duck" on your desk. It doesn't have to be a real rubber duck.

[perrygeo]

But it's funnier if it is.

[madcaptenor]

You can also use an infant. Now that my youngest is two years old this doesn't work any more.