Tonks tilted her head, intent on following him through this plan. It could be aliens. They didn't know. Or evil wizards with a strong Obliviation spell. She wasn't sure. But now she was determined to get to the bottom of this before she woke up.
"Then we can't let them wipe our memories! Isn't tinfoil supposed to prevent alien mindwipes and stuff? Should we make tinfoil hats?" This was probably why Teddy was the alien expert, but Tonks wanted to make tinfoil hats! For protection!