The mishna Uktzin 1:1 discusses yadot (handles) for food, and how they מִטּמא ומְטמא ("contract uncleanness and convey uncleanness"). In his commentary to that mishna, Rambam explains that the yad itself becomes tamei when the food does, and the food becomes tamei when its yad does. Additionally, the yad will convey tumah to anything it touches, if the yad and food are tamei.
This seems like a simple read of the mishna. On the other hand, Tosfot on Ḥullin 128a s.v. beheima beḥayyeha says that yadot don't themselves become tamei. Instead, they transmit tumah to and from the food.
What is the basis of Tosfot's view (eg. how does it make sense with מִטּמא)? More importantly, is there a practical difference between these two views? It seems that according to both views, something tamei touching the combined yad/food anywhere will impart tumah, and anything touching tamei yad/food anywhere will itself become tamei. If the yad breaks off from the food, it's no longer a yad and shouldn't be susceptible to tumah according to either opinion.[source needed]