"the treaty had no teeth in it"
误 We use our tooth for biting and chewing.
正 We use our teeth for biting and chewing.
析tooth的复数是 teeth,这里应该用复数形式。
我妹妹有两把牙刷。误 My sister has two teethbrushes.
正 My sister has two toothbrushes.
析tooth的复数是teeth,但由tooth构成的复合词在变成复数时,则只需将主体名词变成复数形式。