To mend the socks (because, of course, nothing was ever thrown away!!!), people used to stretch the sock — with the hole positioned over the darning mushroom — and sew it up.
The darning mushroom was also called a marzha.

Asa Bartov from Moshav Herut recalls:

“We didn’t even have a darning mushroom for mending socks. My mother would take a glass, stretch the sock over it, and mend it (of course, only after washing it...).”