It has been said that they were once used to open cans. Huh. Just why is unknown, since cans already have pictures on them that tell us what is inside. Further, if cans do not fall apart on command, there have always been power saws and handguns to easily open them. Can openers have been found to have several moving parts to them. But without any instructions printed on them, it is unknown how they were used if they were even used at all. Electric can openers are known, but archaeologists have not been able to find any evidence of electric cans.
Research is ongoing to find out what can openers are all about. Cans have pull tabs today so their relationship to can openers is a complete mystery. In 2019, a researcher opening a can cut his finger, stopping all investigation into can openers until further notice.