There were trackwheels, then rubber balls - which allowed smoother movement, but got gummed up with dirt - and now mini-cameras that film the table top.

先是有了滚轮鼠、然后橡皮球-可允许更平滑地移动，不过容易粘上污垢-现在有了给桌面拍照的微型照相机（译者：指光电鼠标）。

youdao

More than 50 secret mini cameras will be used, some powered by solar panels.

BBC: Ynys-hir nature reserve (Andy Hay RSPB images)

Nigel is now in charge of setting up more than 15 mini-cameras, which takes more preparation than you might think.

BBC: Norfolk - Filming up-close with Springwatch

So, as of today, we have mini copters with cameras.

ENGADGET: And don't forget...