Yes when they do that its wonderful and I am still waiting .......sigh.
A word of warning , please keep da birdy hidden so they cannot get at it unless you are around, cos one naughty cat on here bit the string and swallowed it and is now waiting for his tummy fur to grow back after having to be opened up to look for the string!
They are safe but only when you are there to supervise cos they love them so much