Alan Gilmore: What's bugging Betelgeuse?

One of the brightest stars in the sky is behaving strangely, pulsating from bright to dim twice as quickly as usual.  

At the moment Betelgeuse is very bright in the night. What's going on?  

If anyone knows it'll be Alan Gilmore. Alan's one of our most distinguished astronomers; he once ran the Mt John Observatory and is still involved with the near-asteroid programme at Mt John with his wife, Pam.