I have no idea why, but if you pronounce ‘excuse you’ with a very extended ‘u’ and ‘o’, Reindeer will laugh. If you do this in a variety of funny voices, he will laugh at you for a very long time!
This worked really well yesterday and, as an informal memory test, I decided to try it again today. Happily, it had the same effect today so we did this quite a lot. Including whilst we were out playing in the garden. The neighbours probably think we’re mad!