"Well, sir, the two ran into one another naturally enough at the corner; and then came the horrible part of the thing; for the man trampled calmly over the child's body and left her screaming on the ground." (1.8)
Mr. Hyde commits violence against innocent children without batting an eye.
Mr. Edward Hyde
The other snarled aloud into a savage laugh; and the next moment, with extraordinary quickness, he had unlocked the door and disappeared into the house. (2.36)
Mr. Hyde’s default personality is one of violent savagery.
Mr. Gabriel Utterson
"I have been wanting to speak to you, Jekyll," began the latter. "You know that will of yours?"
A close observer might have gathered that the topic was distasteful; but the doctor carried it off gaily. (3.2)
Dr. Jekyll does not handle unpleasant conversations by resorting to violence, as some people do (i.e., Hyde).
And then all of a sudden he broke out in a great flame of anger, stamping with his foot, brandishing the cane, and carrying on (as the maid described it) like a madman. The old gentleman took a step back, with the air of one very much surprised and a trifle hurt; and at that Mr. Hyde broke out of all bounds and clubbed him to the earth. And next moment, with ape-like fury, he was trampling his victim under foot and hailing down a storm of blows, under which the bones were audibly shattered and the body jumped upon the roadway. (4.1)
Mr. Hyde is unpredictably and excessively violent. His violence is repeatedly likened to animalistic savagery.
Dr. Henry Jekyll
The most racking pangs succeeded: a grinding in the bones, deadly nausea, and a horror of the spirit that cannot be exceeded at the hour of birth or death. (10.4)
Transforming between Dr. Jekyll and Mr. Hyde is not a smooth and seamless process, but rather immensely violent. This signifies the enormity of change that is occurring.
I was conscious, even when I took the draught, of a more unbridled, a more furious propensity to ill. It must have been this, I suppose, that stirred in my soul that tempest of impatience with which I listened to the civilities of my unhappy victim; I declare, at least, before God, no man morally sane could have been guilty of that crime upon so pitiful a provocation; and that I struck in no more reasonable spirit than that in which a sick child may break a plaything. But I had voluntarily stripped myself of all those balancing instincts by which even the worst of us continues to walk with some degree of steadiness among temptations; and in my case, to be tempted, however slightly, was to fall. (10.18)
Mr. Hyde has absolutely no scruples or morals; beating Sir Danvers to death is like a child breaking a plaything—an act of no consequence.
Mr. Edward Hyde
Instantly the spirit of hell awoke in me and raged. With a transport of glee, I mauled the unresisting body, tasting delight from every blow; and it was not till weariness had begun to succeed, that I was suddenly, in the top fit of my delirium, struck through the heart by a cold thrill of terror. A mist dispersed; I saw my life to be forfeit; and fled from the scene of these excesses, at once glorying and trembling, my lust of evil gratified and stimulated, my love of life screwed to the topmost peg. (10.19)
Mr. Hyde (or Dr. Jekyll) derives enormous pleasure from extremely violent acts.
Once a woman spoke to him, offering, I think, a box of lights. He smote her in the face, and she fled. (10.24)
Mr. Hyde is violent even to people who are perfectly civil.