"sibilating" in the verb sense
1. sibilate
pronounce with an initial sibilant
2. sibilate
utter a sibilant
3. hiss, sizz, siss, sibilate
express or utter with a hiss
4. hiss, siss, sizz, sibilate
make a sharp hissing sound, as if to show disapproval
Source: WordNet® (An amazing lexical database of English)
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