mm mammal 哺乳動物 [Card #2; 字卡第2張: 第3個單字]
mm = /m/(2個相同子音在一起, 只發一個音)

Some more examples(更多例字):hammer, stammer, simmer, shimmer, summer, bummer, grammar, gamma, comma, dilemma, common, comment, commence, commerce, commercial, immerse, imminent, immune, immunize, immunization, immediate, communicate, accommodate, consummate, command, commend, recommend, commit, committee, commodity, community, commute, commotion, summon, summit, plummet, grommet, gimmick, mamma, momma, mommy, mummy, dummy, gummy, tummy, yummy, symmetry, summary, scrimmage, rummage, hammock, mammoth, pummel