My Grammar and I (Or Should That Be 'Me'?): Old-School Ways to Sharpen Your English

Sorry, don’t know the plural…
Dear Sir,
Please send me a mongoose.
Oh, by the way, send me another one, too.
In big-game hunting it appears to be fair game to dispense with the usual plurals.
Hence we might shoot several gazelle , two leopard , three lion , three  elephant
and  six  wild  pig  .  This  has  a  slightly  old-fashioned  feel  and  does  somehow
suggest  that  you  are  going  out  to  kill  the  poor  beasts  and  hang  their  heads  on
your wall.
And on the agendum today
Some nouns have no (or a rarely used) singular form:
alms
marginalia tidings

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bellows oats
tongs
billiards pants
trousers
braces pliers
tweezers
clothes scissors
vespers
dregs
shorts
victuals
eaves
thanks
vittles
NB  Nouns  such  as  these  require  a  measure  word  ,  for  example  a  pair  of
trousers, some thanks. You cannot say one scissors . Nor, happily, can you sow
just the one wild oat .