Secret ninja techniques
I believe it was Pat Parker who brought up the idea of reserving the last few minutes of class, after covering the normal curriculum, for what he called the "secret ninja technique of the day". I like the idea (and the name!) so just for fun, I've been doing something along those lines during the morning aikido class.
Once or twice, I'll take something from the higher, koryu kata, which the average green or brown belt hadn't seen yet, but would be simple enough to pull off. Then, sometimes I see something new that, from the outside, looks as if it follows principles well enough (ours at least) and try and see how it feels in practice. This is one we played with today for the last five minutes.
We've done a tenkan (turning) form of tenchinage in our renzoku waza (release chains), but I'd never played with an irimi sort of entry. I'd say it works pretty well, and can come as quite a surprise to uke, even if he's not attacking that hard! Of course, if you try it and get jammed up, you can switch to a tenkan action, turning, switching which hand is up and down and get it that way. I love this stuff!