The 4th stanza (from memory):

The amorous hippopotamus whose love song we know
Is now married and father of ten.
He murmurs "God rot 'em!" as he watches them grow,
And he longs to be single again.
He'll gambol no more by the banks of the Nile,
Which Nasser is flooding next spring.
With hippopoTAmas in silken pyjamas
No more will he teach them to sing...

The switch from the Shalimar to the Nile was inconspicuous in that this stanza was sung, by itself, in the second show (_Another_ Hat).