Science demo ideas?

Oh, and as long as I'm on here, does anyone have ideas for science demos that are appropriate for kindergarden kids? Bossman's recruited me to do science demos at his son's school with the other first year in the lab (who, fairly enough, is not enthused about this extra work).

My current ideas: lemon as a battery, color changing "clock", glow in the dark slime, "elephant toothpaste", and colored smoke (if we can do it outside/we can scrounge up the materials).

Bossman is insistent on doing thermite. Which is super cool (hell, I absolutely still love that demo), but I am convinced we have the potential for half of our audience crying. I am secretly hoping that the department won't let him check out the stuff.

Therefore, we'll probably be doing thermite, but that leaves room for one or two more demos. Bossman has grudgingly approved lemon as a battery.

Any other ideas would be much appreciated.

Help a biochemist out?

Are you doing mol bio or biochem or anything where you're trying to get a mutation to go into a genome?

We've got this system where we can easily get a plasmid with our copy of the gene with the mutation. However, we have to transform into a system where this mutated copy of the gene needs to get into all of the copies of the gene within the native system (otherwise we'll have 75% mutated protein and 25% wild type protein). We've already got antibiotic resistance as a selector, but cells that transform partially still grow. We've got another type of nutrient related selection. But we keep on getting not the full mutation back when we sequence it because our screening system isn't selecting for just the cells where the mutation is in every copy of the gene.

Anyone out there got some awesome ideas for screening? I'm looking and racking my brain, but this is not my field of expertise.