The word rattlesnakes is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 18
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (101 words)
aerates, alkanes, alkenes, anklets, antlers, arsenal, artless, atlases, earless, earnest, eastern, elaters, enseals, ensears, enteral, entreat, estates, eternal, kernels, kestrel, kettles, lateens, latents, leakers, leaners, leanest, leasers, letters, natters, nearest, neatest, nesters, nestles, netless, netters, nettles, rankest, rattles, realest, relates, relents, renests, rentals, resales, reseals, reseats, resents, reslant, restake, restate, retaken, retakes, retasks, retaste, retests, saltate, saltern, sateens, sealant, sealers, searats, seastar, seaters, senates, sensate, setters, settler, settles, skaters, skelter, slaters, sneaker, stalest, stalker, starlet, startle, staters, stealer, sterane, sternal, stratas, streaks, streets, talents, talkees, talkers, tankers, tarsals, tartans, taskers, tasters, tealess, teasels, teasers, telnets, tensest, tenters, ternate, tersest, testers, trestle