Occasionally they would hear a harsh croak or a splash as some amphibian was disturbed, but the only creature they saw was a toad as big as Will's foot, which could only flop in a pain-filled sideways heave as if it were horribly injured. It lay across the path, trying to move out of the way and looking at them as if it knew they meant to hurt it.
'It would be merciful to kill it,' said Tialys.
'How do you know?' said Lyra. 'It might still like being alive, in spite of everything.'
'If we killed it, we'd be taking it with us,' said Will. 'It wants to stay here. I've killed enough living things. Even a filthy stagnant pool might be better than being dead.'
'But if it's in pain?' said Tialys.
'If it could tell us, we'd know. But since it can't, I'm not going to kill it. That would be considering our feelings rather than the toad's.'
They moved on.

Philip Pullman