And it is thought that John was writing in opposition of what came to be known as Docetism, as regards the belief that "Christ's body was not human but either a phantasm or of real but celestial substance, and that therefore his sufferings were only apparent," (Oxford Languages) and "Broadly it is taken as the belief that Jesus only seemed to be human, and that his human form was an illusion." (Wikipedia).
Related to this, you have a religion which does profess that the Divine Christ came in the flesh, being literally incarnated, and thus not only appeared as human but whose flesh and blood would scientifically appear to be just what it was, human. Thus the emphasis upon the physicality of Christ in John and elsewhere. Luke 24:39; John 1:14; John 20:20,25,27; 1 Jn. 1:1; 1 John 5:6). But which religion also asserts, that at the utterance of words of consecration by their priest, then this Christ becomes locally really present, flesh, blood soul and divinity, under the mere appearance bread and wine (either of, and wholly present in any fragment of either and both), and at which moment the bread and wine no longer not exist, their substance being changed into the same body of Christ as was crucified.
And which is to be believe despite appearance to the contrary, and even though what is visible would scientifically appear to be just what it appears to be, bread and wine, for unlike the incarnated Christ, "The presence of Christ's true body and blood in this sacrament cannot be detected by sense, nor understanding, but by faith alone..." (Summa Theologica; 75:1) Thus "If you took the consecrated host to a laboratory it would be chemically shown to be bread, not human flesh." (Dwight Longenecker, "Explaining Transubstantiation")
But which "Real Presence" only locally lasts/exists until the non-existent bread and or wine begins to manifest (appearance being critical) decay/corruption, at which point Christ is no longer locally present.
And which relates to another problem, that of microscopic particles of the consecrated bread and wine, since these can end up in a vacuum cleaner. Thus it appears that this is a matter of dispute. For while it is stated by the American bishops, "Christ is wholly present in any fragment of the consecrated Host or in any drop of the Precious Blood", (Question #12: https://www.usccb.org/resources/The%20Real%20Presence%20of%20Jesus%20Christ%20in%20the%20Sacrament%20of%20the%20Eucharist.pdf) it is also held that "those particles which are so small as to be invisible to the human eye, or to be indistinguishable from a particle of dust – these cannot any longer be the Eucharist," "those microscopic particles which fall from the Host are not the Eucharist, since they clearly do not retain the appearance of bread." (http://newtheologicalmovement.blogspot.com/2012/07/fragments-of-eucharistic-species.html)
In any case, the Son of God never appeared as an intimate object which can be handled by man, and after His incarnation then He always appeared in bodily form, and on earth at least then it was one of manifest physicality. Thus the Catholic Eucharist is akin to a Docetist type Christ, whose appearance does not correspond to what He bodily was, and would scientifically test to be, and instead it is also one who feels no physical pain by being chewed and digested.