The word rattlesnake 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: 17
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (59 words)
aerates, alkanes, alkenes, anklets, antlers, arsenal, earnest, eastern, elaters, enteral, entreat, eternal, kernels, kestrel, kettles, lateens, latents, leakers, leaners, leanest, letters, natters, nearest, neatest, netters, nettles, rankest, rattles, realest, relates, relents, rentals, reslant, restake, restate, retaken, retakes, retaste, saltate, saltern, sealant, settler, skelter, sneaker, stalker, starlet, startle, stealer, sterane, sternal, talents, talkees, talkers, tankers, tartans, telnets, tenters, ternate, trestle