We take an opportunity to consider receiving communion well, with greater love and devotion. It is also good to note that Jesus only distributes communion under the one species of the Host -- whereas, on Holy Thursday, he gave communion under both kinds (the Host and the Chalice) as he was distributing to his apostles whom he had just ordained as priests; here, when distributing communion to the lay faithful (Cleopas and the other), our Lord only gives communion under the species of his Body. The whole Jesus is present in the Host and in the Chalice: Body and Blood, Soul and Divinity, and the fullness of grace is received under Host alone. Indeed, the Church teaches that there is nothing "less" in receiving only the Host, nor is there any "more grace" in receiving the Chalice.
Although not all of the following norms are specified in the sermon, it is good to make note of certain guidelines under which the Chalice is permitted to be distributed. First and foremost, we recognize that the general norms of the Church do not permit the distribution of the Chalice except in the most unusual circumstances (e.g. when people make First Communion, Religious Profession, to the couple who gets married). In the United States, wider permission was given (by a special indult from the Vatican and only with the dispensation of the local bishop and the wise discernment of the pastor) for communion to be distributed under both kinds -- but the following norms must be observed.
From "Redemptionis Sacramentum", Vatican Congregation for Divine Worship from 2004 (paragraphs 100-107):
"[Distribution of the Chalice] is to be completely excluded where even a small danger exists of the sacred species being profaned."
"The chalice should not be ministered to lay members of Christ’s faithful where there is such a large number of communicants that it is difficult to gauge the amount of wine for the Eucharist and there is a danger that more than a reasonable quantity of the Blood of Christ remain to be consumed at the end of the celebration."
"[The Chalice is not to be distributed] where a notable part of the people continues to prefer not to approach the chalice for various reasons, so that the sign of unity would in some sense be negated."
"In accordance with what is laid down by the canons, 'one who throws away the consecrated species or takes them away or keeps them for a sacrilegious purpose, incurs a latae sententiae excommunication reserved to the Apostolic See; a cleric, moreover, may be punished by another penalty, not excluding dismissal from the clerical state'. To be regarded as pertaining to this case is any action that is voluntarily and gravely disrespectful of the sacred species. Anyone, therefore, who acts contrary to these norms, for example casting the sacred species into the sacrarium or in an unworthy place or on the ground, incurs the penalties laid down."
Additionally, the USCCB states that where there would regularly be more lay people serving as extraordinary ministers of holy communion than three are priests and deacons serving as ordinary ministers, it may be fitting to not distribute the Chalice so as to avoid the appearance that it is ordinary or normal for lay minsters to distribute communion. (cf. Norms for the Distribution and Reception of Communion under Both Kinds)
What does this mean? That if there is any danger that the Chalice might be spilt, communion should be given only under the Host. If there is a large number of people at the Mass so that it is difficult to estimate very exactly how much wine to use, communion should be given only under the Host. If say 20% of the people don't want to receive from the Chalice, communion should be given only under the Host. If there are not a number of priests and deacons so that they would generally outnumber the lay extraordinary ministers, communion should probably be given only under the Host.
Finally, the care of the Precious Blood is such a serious matter, that those who have poured the remaining Blood down the drain or into the ground are subject to an excommunication which even the Bishop cannot lift -- and this abuse is something which many of us know from experience to have been shockingly common in certain places and times over the past 50 years.