The human brain is like the roots of a tree. A series of entangled networks. And due to this complex network, we recall memories that have been instigated from any of your 5 senses. But could we try and erase 1 part of our memory? Or could we cut down the network to that memory?
There are several nerves in our brain, which connect to our memory. In this movie after Clementine erases her memories related to Joel, there were yet some factors that were going back to her memory of Joel but, she wasn’t sure what was it. As it had all gone from her conscious mind, but her subconscious mind still possessed those memories.