The law presumes all persons to be sane ( People v. Dunigan (1981), 96 Ill. App.3d 799; People v. Dominique (1980), 86 Ill. App.3d 794), but a defendant may overcome that presumption by presenting some evidence to raise a reasonable doubt of his or her sanity, and when such defense has been raised, the presumption no longer prevails and the State must prove beyond a reasonable doubt that the defendant was sane at the time of the alleged offense. ( People v. Jones (1982), 109 Ill. App.3d 120.)Insanity of a person either before or after the commission of a crime cannot excuse the crime; only insanity existing at the very time of the crime can excuse it. ( People v. Smith (1984), 124 Ill. App.3d 243, 250; People v. Dunigan (1981), 96 Ill. App.3d 799, 820.) An accused who understood the nature of his or her conduct and appreciated its wrongfulness will still be excused from criminal liability if his or her ability to consciously refrain from that conduct was substantially impaired by a mental disease or defect.

We find a rational trier of fact could have found that defendant was consciously aware that his conduct was practically certain to result in injury to Joel. See People v. Smith, 124 Ill. App. 3d 243, 247-48 (1984) (in affirming the defendant's conviction for aggravated battery, this court found the defendant should have been "consciously aware" brandishing a knife and refusing to relinquish it to the victim had the natural and probable consequence of causing injury to the victim rather than finding it to be an accidental injury). ¶ 31 Defendant further argues that his conviction should be reversed because the court did not find that the knife which caused injury to Joel was a "deadly weapon." We disagree.

¶ 35 "Knowledge, due to its very nature, is ordinarily proven by circumstantial evidence, rather than by direct proof." People v. Smith , 124 Ill. App. 3d 243, 248, 79 Ill.Dec. 781, 464 N.E.2d 685 (1984). To prove knowledge by circumstantial evidence, the State must present sufficient facts from which an inference of knowledge can be made.

) The mental state of knowledge is ordinarily proven by circumstantial evidence, as opposed to direct proof. People v. Smith (1984), 124 Ill. App.3d 243, 248, 464 N.E.2d 685, 688. • 11 Here, the defendant admitted that he knew he was purchasing the truck from someone not listed on the certificate of title, yet he claimed that he believed the certificate of title was complete.

Ordinarily, this element of intent is established by circumstantial evidence. People v. Traylor (1985), 139 Ill. App.3d 443, 447, 487 N.E.2d 1040; People v.Smith (1984), 124 Ill. App.3d 243, 248, 464 N.E.2d 685. • 2 We have reviewed the evidence and determine that it is sufficient to prove defendant guilty beyond a reasonable doubt of the offense of aggravated battery of a child.

People v. Young (1978), 60 Ill. App.3d 351, 353, 376 N.E.2d 739." ( People v. Smith (1984), 124 Ill. App.3d 243, 250, 464 N.E.2d 685.) Furthermore, the weight given an expert's opinion is based on his reasoning and the facts he uses to support his opinion.