Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ob-murmŭro, āvi, ātum, 1, v. n., to murmur against, at, or to (poet. and in post-Aug. prose); constr. with dat. or acc.: precibusque meis obmurmurat ipse, Ov. H. 18, 47: itidem obmurmurasse: Τί γάρ μοι, etc., Suet. Oth. 7: Pharisaei, quod, etc., Ambros. Cain et Abel, 2, 4, 16: obmurmurando dicere (with object-clause), Front. 4, 6, 2.