ἐμπνέων ... Present active participle of old and common verb. Not “breathing out,” but “breathing in” (inhaling) as in Aeschylus and Plato or “breathing on” (from Homer on). -- Robertson, A. T. (1933). Word Pictures in the New Testament (Ac 9:1). Broadman Press.
Acts 9:1 (ESV) But Saul, still breathing threats and murder against the disciples of the Lord, went to the high priest
It is difficult to find an example of usage related to here in Acts. It occurs once in the New Testament, and in the Septuagint (LXX) it refers to people who are alive (breathing). Breathing in seems to give more of the picture of a hound dog tracking a sent than a bull expressing anger.
Appendix: looking for meanings other than simply breath that might apply herea
Philo uses this word:
And God breathed into man’s face both physically and morally. Physically, when he placed the senses in the face: and this portion of the body above all others is vivified and inspired; and morally, in this manner, as the face is the dominant portion of the body, so also is the mind the dominant portion of the soul. It is into this alone that God breathes; but the other parts, the sensations, the power of speech, and the power of generation, he does not think worthy of his breath, for they are inferior in power. (40) By what then were these subordinate parts inspired? -- Yonge, C. D. with Philo of Alexandria. (1995). The works of Philo: complete and unabridged (p. 29). Hendrickson.