1) The plural of mongoose shall be mongeese. I care for neither dictionary nor derivation. They are mongeese.
2) The past participle of fit shall be fat, following the hallowed pattern of sit/sat and shit/shat.
3) The plural of toothbrush shall be toothbri. I don't know why, in fact I hate Latin pluralisations. Perhaps I feel that it should be teethbrushes, senseless though that may be. Mrs Malaprop suggests toothbroi and I would be willing to compromise. But I abhor toothbrushes.
Once my three whimsies are acceded to by all speakers of English, I shall reveal the terrible truth of snuck.