Make your own pet cloud

You will need:

A large glass storage jar. 'Kilner' jars are good - they're the type with the big levered glass lid and a rubber sealing grommet. It's easiest to do the demonstration if you remove the lid completely, but it's not essential.
A rubber glove. Yes, you read that correctly.
A box of matches. Remember all the things everyone always says about playing with matches; be careful, and make sure there's someone else around who's more sensible than you are. That usually - but not always - means 'an adult.'
A cup of water.

What you do:

Tip the water into the jar and swirl it around a bit. Now light a match, hold it over the neck of the bottle while it flares and settles down, then blow it out again. Let some of the smoke fall into the jar, then drop the match in so it's safely quenched in the water.
Now comes the harder part: dangle the rubber glove into the jar, and stretch the cuff over the neck so it seals. This can be a bit fiddly, but you need the glove to be good and tight over the jar.
The final part is simple enough, but very hard work: hold the jar down with one hand, and with the other grab the inside of the glove. Pull the glove sharply out of the jar - you'll have to yank really hard. Don't slip and drop the jar on your foot, it'll hurt.
With a little luck, you'll see a cloud form in the jar. Wooo! When you let go of the glove, your pet cloud will evaporate back into water vapour - but it'll return if you pull the glove again.

What's going on?

Firstly, it's a genuine cloud in there. No, really. You might see it more clearly if you light the jar from one side with a desk lamp, and place some dark card behind it, but I have had this work quite clearly in plain daylight.

When you pull the glove, you reduce the pressure of the air inside the jar. That reduces the amount of water vapour (gas) that can be carried in the air; the water vapour then condenses into droplets of liquid. It'll tend to do this on the sides of the jar or the water surface at the bottom, but if there are a few small particles floating around - like smoke - it'll tend to form droplets on those instead.

That floating mass of tiny water droplets is... a cloud. Clouds form where the air temperature or pressure is just a little lower than is needed to keep the water as a gas. Which, in this case, is inside your jar.

Look after your pet cloud, and let me know if you manage to teach it any tricks. Other than hide-and-seek, of course.