They were chewing a thick tough unleavened bread, not the sort of light and airy communion wafer we are served today. Also, the Lord was in a hurry. Time was short. Judas had just left to denounce him and he wanted sufficient time to pray to his Father before his arrest.
Apparently the Greek implies something like: “Take this and eat it right away.” See Kenneth S. Wuest, ‘The New Testament - An Expanded Translation,’ p.69:
“Take at once. Eat at once. This is my body” - Matthew 26.26
Today (at least in my church) we are eating something far less substantial than unleavened bread, and there is no need for us to hurry.