In LLPSI Capitoluim XLII (Exercitium 11) Orberg is testing on use of Gerundive and, seemingly, is providing as a hint the Gerund counterpart. Here is one example:
2. Dido puero intuendo incenditur.
So Dido puero intuendo incenditur is Gerundive and means something like Dido, 'The boy having to be looked at, was inflamed'.
The explanation in square brackets suggests that, using a gerundive, this would be written:
Dido puerum intuendo incenditur which means ...