Using yeast cake from previous brew

As mentioned a couple of days ago, I had the bright idea of pitching a couple of Coopers tins and DME into the remains of Dave's IPA.

After kegging the IPA, I thought it'd be good to reuse the yeast, and eke out whatever hop aroma remained in the pellet residue and hop bag. So, just tip in some more fermentables and off we go...

All good.... in theory.  What I didn't count on was the explosive activity of the yeast.  After a fermentation, the yeast count has increased exponentially.... and they're still very much active and raring to go.

So, coupling this with more malt than I probably should have used, it all frothed up and out the airlock. Messy.
The scary bit, however, was the airlock regularly becoming blocked with hop residue. This resulted in increased pressure in the fermenter.
A quick word of advice..... if the airlock has stopped bubbling, but fermentation is visibly underway, be very, very careful when taking the bung out. It's difficult cleaning green and brown gunk off the ceiling....